JP2008039394A - Electromagnetic induction sensor for metal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic induction sensor that generates a metal piece detection signal only when a metal piece is mixed in an object to be inspected in a metal piece detection sensor of a metal piece detection device.
An electromagnetic induction sensor includes an excitation coil and a detection coil. Both coils are arranged so that their coil surfaces are orthogonal to each other. The electromagnetic induction sensor is placed so that the coil surface of the excitation coil 21 is perpendicular to the object to be inspected 31 and the coil surface of the detection coil 22 is parallel. The exciting coil 21 generates a uniform magnetic field on the inspection object 31. Therefore, the metal detection signal is generated in the detection coil 22 only when the metal piece is mixed in the inspection object 31. [Selection]

Description

  The present invention relates to an electromagnetic induction sensor used in a detection device, a landmine detection device, or the like for a metal piece mixed in or latent in food, industrial materials, clothes, mail, or the like.

Conventionally, an electromagnetic sensor is used in a detection device for a metal piece mixed in food, industrial material, or the like.
A conventional electromagnetic sensor will be described with reference to FIG. 7 (see, for example, Patent Document 1).
FIG. 7 shows an electromagnetic sensor arranged on the object to be inspected, FIG. 7 (a) is a plan view, FIG. 7 (b) is a cross-sectional view in the arrow direction of the X1 portion of FIG. 7 (c) is a plan view of the back surface of the electromagnetic sensor.
In FIG. 7, 11 is an electromagnetic sensor, and 13 is a belt of a belt conveyor that conveys the inspection object 12. In the electromagnetic sensor 11, a sensor coil 112 is wound around an iron core 111 having an E-shaped cross section, and a permanent magnet 113 is attached to the center. The sensor coil 112 of the electromagnetic sensor 11 is connected to an AC power source (not shown) and a detection circuit (not shown). The inspection object 12 is conveyed in the X2 direction by the belt 13 and moves under the electromagnetic sensor 11.
When an AC power source is connected to the sensor coil 112, an AC current flows through the sensor coil 112 to generate an alternating magnetic field, and the magnetic flux of the sensor coil 112 passes through a magnetic path including the belt 13. When a metal piece is mixed in the inspection object 12, if the inspection object 12 moves below the electromagnetic sensor 11 as shown in FIG. 7, the magnetic characteristics of the magnetic path of the sensor coil 112 change. The amplitude of the alternating current 112 changes. The change in the amplitude is extracted by the detection circuit, and the metal piece mixed in the inspection object 12 is detected.

JP 2004-85439 A

  Since the conventional electromagnetic sensor 11 of FIG. 7 uses one sensor coil 112 as an excitation coil and a detection coil, a metal piece is mixed in the inspection object 12 in the detection coil (sensor coil 112). Even when there is no current. That is, even when no metal piece is mixed, a detection signal is generated in the detection coil. Therefore, in order to detect a metal piece, an amplitude difference between both detection signals must be extracted as a metal piece detection signal from a detection signal when the metal piece is not mixed and a detection signal when the metal piece is mixed. Don't be. For this reason, the extraction of the metal piece detection signal requires complicated signal processing using a complex circuit such as a bridge circuit (balanced circuit), which complicates the metal piece detection device. Further, when the distance (interval) between the object to be inspected 12 and the sensor coil 112 is increased, both the detection signals are reduced, and the amplitude difference between the two detection signals is also reduced.

Further, in the conventional electromagnetic sensor, when a metal piece is mixed in the inspection object 12, the current of the detection coil also changes when the distance (distance) between the sensor coil 112 and the inspection object 12 changes. It affects the metal piece detection signal and lowers the detection accuracy and detection sensitivity of the metal piece. The change in the distance (distance) between the sensor coil 112 and the object to be inspected 12 is caused by the vertical movement of the position of the sensor coil 112 or the difference in the position of the metal piece mixed in the object to be inspected 12 (e.g. This is caused by a difference between whether the sensor coil 112 is close to or far from the sensor coil 112.
In order to solve the above-described problems of the conventional magnetic sensor, the present invention generates a detection signal in the detection coil (generates a metal detection signal) only when a metal piece is mixed in the object to be inspected. The purpose is to provide.

In order to achieve the object of the present invention, in the electromagnetic induction sensor of the metal detection device according to claim 1, the excitation coil and the detection coil are arranged so that the coil surfaces of both coils intersect, and the coil surface of the detection coil Are arranged in parallel to the object to be inspected.
The electromagnetic induction sensor of the metal detection device according to claim 2 is the electromagnetic induction sensor of the metal detection device according to claim 1, wherein the detection coil is formed by juxtaposing a plurality of detection coils.
According to a third aspect of the present invention, in the metal detection method, the induction coil and the detection coil are arranged so that the coil surfaces of the two coils cross each other, so that the coil surface of the detection coil of the electromagnetic induction sensor is parallel to the object to be inspected. A metal piece of the inspection object is detected by moving the sensor or the inspection object.
A metal detection method according to a fourth aspect of the present invention is the metal detection method according to the third aspect, wherein the detection coil includes a plurality of detections juxtaposed.

  The detection coil of the electromagnetic induction sensor of the present invention generates a detection signal only when a metal piece is mixed in the object to be inspected (that is, a metal piece detection signal is generated), and no metal piece is mixed. Since no detection signal is generated, the metal piece can be reliably detected even when the amplitude of the metal piece detection signal is small. Therefore, the metal piece can be detected with higher accuracy and sensitivity than the conventional metal piece detection sensor. Moreover, since the metal detection apparatus using the electromagnetic induction sensor according to the present invention can easily extract the metal piece detection signal, the extraction circuit for the metal piece detection signal can be easily configured.

Since the amplitude of the metal piece detection signal of the electromagnetic induction sensor of the present invention varies depending on the size of the metal piece, when the type (material) of the metal piece is the same, the metal piece detection signal varies depending on the amplitude of the metal piece detection signal. Can be estimated. Further, since the phase of the metal piece detection signal is determined by the type (material) of the metal piece regardless of the dimension of the metal piece, the type (material) of the metal piece can be estimated from the phase of the metal piece detection signal.
In the electromagnetic induction sensor of the present invention, even if the distance (interval) between the electromagnetic induction sensor and the metal piece changes to change the amplitude of the metal piece detection signal, the change in the amplitude is not related to the determination of the presence or absence of the metal piece. The presence / absence of the metal piece is not erroneously determined by the fluctuation of the amplitude of the metal piece detection signal.

An embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is used for the part common to each figure.
FIG. 1 shows an electromagnetic induction sensor arranged on an object to be inspected. 1A is a plan view, FIG. 1B is a side view in the Y2 direction of FIG. 1A, and FIG. 1C is a cross-sectional view of the Y1 portion of FIG. It is.
In FIG. 1, 21 is an excitation coil of the electromagnetic induction sensor, 22 is a detection coil of the electromagnetic induction sensor, and 31 is an object to be inspected.
The exciting coil 21 is a rectangular (rectangular) coil, and the detection coil 22 is a pancake (donut-shaped) coil. The electromagnetic induction sensor includes an excitation coil 21 and a detection coil 22. The excitation coil 21 and the detection coil 22 are arranged so that the coil surfaces of the respective coils are orthogonal (intersect), and the excitation coil 21 has its coil surface. Is installed so as to be orthogonal to the inspection object 31. Therefore, the coil surface of the detection coil 22 is parallel to the inspection object.
Here, the coil surface is a surface orthogonal to the central axis of the coil (opening surface surrounded by the windings). The same applies hereinafter.

FIG. 2 is a diagram for explaining the direction of the magnetic flux generated by the exciting coil 21 and the positional relationship between the metal piece in the inspection object and the detection coil.
When a current is passed through the exciting coil 21, as shown in FIG. 2A, the exciting coil 21 generates a uniform magnetic field in a direction perpendicular to the winding direction (direction perpendicular to the coil surface), and the direction is parallel. Generate the same magnetic flux Mf. Since the detection coil 22 is placed in a uniform magnetic field as shown in FIG. 2B, an electromotive force is induced by the magnetic flux Mf. At this time, the detection coil 22 has symmetrical portions 22l and 22r on both sides of the center line Y3 parallel to the magnetic flux Mf of the coil. Therefore, as shown in FIG. When not mixed, the electromotive force induced in the left portion 22l of the detection coil 22 and the electromotive force induced in the right portion 22r have the same magnitude and opposite directions. Therefore, the electromotive force induced in the left portion 22 l and the electromotive force induced in the right portion 22 r cancel each other, and no detection signal is generated in the detection coil 22. That is, when no metal piece is present in the uniform magnetic field, no detection signal is generated in the detection coil 22.

  On the other hand, when a metal piece is mixed in the inspection object 31, for example, as shown in FIG. 2C, when a metal piece 32 is mixed in the inspection object 31, the metal piece 32 is caused by the magnetic flux Mf. Eddy current i is generated. Therefore, the spatial magnetic field in the vicinity of the metal piece 32 is affected by the magnetic field generated by the eddy current i, and the uniform magnetic field is disturbed. The eddy current i flows in the opposite direction between the front end portion 32 a and the rear end portion 32 b of the metal piece 32.

  In the case of FIG. 2C, the detection coil 22 is located away from the metal piece 32, so that even if the spatial magnetic field near the metal piece 32 is disturbed, it is not affected. That is, no detection signal is generated in the detection coil 22. Next, when the electromagnetic induction sensor is moved in the arrow Y4 direction with respect to the inspection object 31, and the detection coil 22 advances to the front end portion 32a of the metal piece 32 as shown in FIG. Because of the influence of the magnetic field generated by the eddy current i, an electromotive force is induced. That is, a metal piece detection signal is generated in the detection coil 22. When the detection coil 22 further advances and as shown in FIG. 2 (e), the detection coil 22 generates an eddy current i in the front end portion 32a and the rear end portion 32b of the metal piece 32. Influenced by magnetic field. At this time, since the directions of the eddy currents i of the front end portion 32a and the rear end portion 32b are opposite, no detection signal is generated in the detection coil 22. When the detection coil 22 advances to the position of FIG. 2F, the detection coil 22 is affected by the magnetic field generated by the eddy current i of the rear end portion 32b of the metal piece 32. Is induced. That is, a metal piece detection signal is generated in the detection coil 22. In that case, the polarity of the metal piece detection signal is opposite to that of the metal piece detection signal of FIG.

As described above, the detection coil 22 of the electromagnetic induction sensor of FIG. 1 generates a metal piece detection signal only when the metal piece 32 is mixed in the inspection object 31, and when the metal piece 32 is not mixed. No detection signal is generated. That is, the detection signal of the detection coil 22 = the metal piece detection signal. Therefore, the electromagnetic induction sensor of FIG. 1 extracts the amplitude difference between the detection signal when the metal piece 32 is not mixed and the detection signal when the metal piece 32 is mixed, as in the conventional electromagnetic sensor. There is no need to extract a metal piece detection signal. The electromagnetic induction sensor of FIG. 1 generates a metal piece detection signal only when the metal piece 32 is mixed in the object 31 to be inspected. Even if the amplitude of the piece detection signal fluctuates, the fluctuation of the amplitude is not related to the detection of the presence or absence of the metal piece, and therefore the determination of the presence or absence of the metal piece does not occur.
Although FIG. 2 demonstrated the example which moves an electromagnetic induction sensor to the arrow Y4 direction, you may move the to-be-inspected object 31 instead of moving an electromagnetic induction sensor.

Here, the test result of the electromagnetic induction sensor of FIG. 1 will be described.
In the test of the electromagnetic induction sensor, the electromagnetic induction sensor of FIG. 1 was installed on a metal piece, a high frequency signal was applied to the excitation coil 21, the electromagnetic induction sensor was moved, and the voltage induced in the detection coil 22 was measured. When no metal piece was present, no voltage was induced in the detection coil 22.
FIG. 5 shows the voltage induced in the detection coil 22. In FIG. 5, the horizontal axis indicates the in-phase component of the voltage induced in the detection coil (the component in phase with the excitation current), and the vertical axis indicates the 90-degree phase advance component (excitation current and 90-degree phase advance component). FIG. 5 shows the normalized voltage.

The metal pieces used were the bolts (FIG. 6 (a)), clips (FIG. 6 (b)), and staples (FIG. 6 (c)) of FIG. Clips and staples are of substantially the same type (material), but bolts are different in type (material).
The exciting coil 21 has a length (a dimension in a direction perpendicular to the central axis of the coil facing the object to be inspected) 160 mm, a height of 30 mm, and a width (a central axis of the coil facing the object to be inspected). The dimensions of the detection coil 22 are an outer diameter of 70 mm, a winding width of 10 mm, and a winding thickness of 1 mm.
The dimensions of the bolts are as follows: the bolt is 50 mm long, the head diameter is 16 mm, the screw diameter is 10 mm, the clip (b) is 50 mm long, the width is 10 mm, the clip (b) is 28 mm long, the width is 8 mm, and the clip (c) Has a length of 21 mm, a width of 5 mm, and a stapler needle having a length of 9 mm and a width of 1 mm.

FIG. 5A shows a metal piece detection signal of a bolt and a metal piece detection signal of a clip (A). The bolt metal piece detection signal and the clip (A) metal piece detection signal have different amplitudes and different phases.
FIG. 5B shows metal piece detection signals of clips (A) to (C). The metal piece detection signals of the clips (A) to (C) have smaller amplitude but smaller phase as the size of the clip is smaller. That is, when the size of the metal piece changes, the amplitude of the metal piece detection signal changes, but the phase does not change.

FIG.5 (c) shows the metal piece detection signal of a staple. In the case of a staple, the amplitude of the metal piece detection signal is small, but it can be detected with high sensitivity like a bolt or a clip. The phase is the same as that of the clip.
According to the test result of FIG. 5, since the detection coil generates a metal piece detection signal only when there is a metal piece, the metal piece can be reliably detected even when the amplitude is small. It can also be seen that the amplitude of the metal piece detection signal varies depending on the size of the metal piece, but the phase does not change (the same). And it turns out that the phase of a metal piece detection signal changes with the kind (material) of a metal piece. From this, when the type (material) of the metal piece is the same, the size of the metal piece can be estimated from the amplitude of the metal piece detection signal, and the type of metal piece ( Material) can be estimated.

Next, the winding direction of the detection coil and the shape of the detection coil will be described with reference to FIG.
The winding of the exciting coil 21 in FIG. 3A is wound in a direction orthogonal to the moving direction Y4 of the electromagnetic induction sensor, like the exciting coil 21 in FIG. Further, the winding of the exciting coil 21 in FIG. 3B is wound in a direction parallel to the moving direction Y4 of the electromagnetic induction sensor. Since the metal piece detection signal may differ depending on the shape and direction of the metal piece mixed into the object to be inspected, the electromagnetic induction sensor of FIG. 3A and the electromagnetic induction sensor of FIG. When used, a more stable metal piece detection signal can be obtained.
The detection coil 22 may have a rectangular (quadrangle) shape as shown in FIG.

FIG. 4 shows an example of an electromagnetic induction sensor that can inspect a wide range of an object to be inspected at a time.
In the electromagnetic induction sensor of FIG. 4A, a plurality of pancake-like detection coils 22 are juxtaposed in the winding direction of the detection coil 22. The electromagnetic induction sensor shown in FIG. 4A can inspect a wide range of the entire width of the inspection object 31 at a time, and determines the position where the metal piece is mixed by the detection coil 22 from which the metal piece detection signal is detected. be able to. The electromagnetic induction sensor in FIG. 4B is an example in which one long rectangular detection coil 22 is used instead of the plurality of detection coils 22 in FIG. The electromagnetic induction sensor shown in FIG. 4B can inspect a wide range of the inspection object with one detection coil, but cannot determine the position of the metal piece.
The electromagnetic induction sensor in FIG. 4C is the same as the electromagnetic induction sensor in FIG. 4A except that the electromagnetic induction sensor in FIG.

It is the top view of the electromagnetic induction sensor which concerns on the Example of this invention, a side view, and sectional drawing. It is a figure explaining the positional relationship of the direction of the magnetic flux which the exciting coil of the electromagnetic induction sensor of FIG. 1 generate | occur | produces, and the metal piece and detection coil in a to-be-inspected object. The example which changed the direction of the winding of the exciting coil of the electromagnetic induction sensor of FIG. 1 and the example which changed the shape of the detection coil are shown. FIG. 1 shows a modification of the electromagnetic induction sensor of FIG. 1 and an electromagnetic induction sensor capable of performing a wide range of inspections at once. The test result of the electromagnetic induction sensor of FIG. 1 is shown. The shape of the metal piece used for the test of FIG. 5 is shown. It is the top view, side view, and sectional drawing of the conventional electromagnetic sensor.

Explanation of symbols

21 Excitation coil 22 of electromagnetic induction sensor Detection coil 22l of electromagnetic induction sensor 22l Left side portion 22r of detection coil 22 Right side portion 31 of detection coil 22 Inspected object 32 Metal piece 32a mixed in inspected object Front end portion 32b Rear end portion Mf of metal piece 32 Magnetic flux i generated by exciting coil 21 Eddy current

Claims (4)

  An electromagnetic induction sensor for a metal detector, wherein an excitation coil and a detection coil are disposed so that the coil surfaces of both coils intersect, and the coil surface of the detection coil is disposed in parallel with an object to be inspected.   The electromagnetic induction sensor of the metal detection apparatus according to claim 1, wherein the detection coil is formed by juxtaposing a plurality of detection coils.   Inspected by moving the electromagnetic induction sensor or the inspection object so that the coil surface of the detection coil of the electromagnetic induction sensor is arranged so that the coil surfaces of the excitation coil and the detection coil intersect each other. A metal detection method for detecting a metal piece of an object.   The metal detection method according to claim 3, wherein the detection coil is formed by juxtaposing a plurality of detections.