JP2009092599A - Metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detecting sensitivity irrespective of the shape of metal to be detected and to reduce the number of parts. <P>SOLUTION: This metal detector 1 includes: a permanent magnet 4 arranged to locate a magnetic pole along a Z-axis direction; a core part 2 having a magnetic core 2a formed in approximately plate shape along Y-Z planes and formed with an end face 7a approximately perpendicular to a Z-axis, and a magnetic core 2b formed in approximately plate shape along the Y-Z planes and formed with an end face 7b on the same plane including the end face 7a, and integrating the magnetic cores 2a, 2b at the ends opposite to the end faces 7a, 7b; and a coil 3 wound around the magnetic core 2b. The permanent magnet 4 is arranged in proximity to a side face 8, opposite to the magnetic core 2b, of the magnetic core 2a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal detection apparatus that detects an inspection object such as a metal piece contained in an object to be detected.

A technique for detecting metal pieces such as stainless steel scraps generated from a manufacturing apparatus or the like mixed in an object such as food or electronic parts is indispensable for ensuring food safety and reliability of electronic parts. This type of conventional technology includes a device that generates a high-frequency electromagnetic field from a coil and detects the change in the impedance of the coil due to the eddy current of the resulting metal piece, and detects magnetic metal using electromagnetic induction. There are known devices and the like. As a device like the latter, the following Patent Document 1 discloses a coil arranged in parallel with the moving direction of the object, a coil arranged so as to surround the moving path of the object perpendicular to the coil, and these coils. A metal detector including a magnet that generates a magnetic flux penetrating a coil is disclosed.
Japanese Patent Laid-Open No. 9-80162

  However, when detecting a change in the impedance of the coil as described above, it has been difficult to detect with high sensitivity a metal piece mixed in a metal part such as an aluminum package or an object containing a large amount of salt. On the other hand, when detecting the induced electromotive force due to electromagnetic induction as in the metal detector described in Patent Document 1, in order to maintain the detection sensitivity according to the direction and moving direction of the metal piece, the shape of the metal piece is used. It is necessary to redesign the coil arrangement accordingly. Moreover, since it is necessary to pass an object through the inside of a coil, an apparatus structure becomes complicated.

  Therefore, the present invention has been made in view of such a problem, and provides a metal detection device capable of improving detection sensitivity and reducing the number of parts regardless of the shape of a metal to be detected. For the purpose.

  In order to solve the above-described problems, a metal detection device of the present invention has a permanent magnet arranged so that a magnetic pole is positioned along a predetermined direction and a substantially plate shape along the predetermined direction. A first magnetic core having a first end surface substantially perpendicular to the first magnetic core, and a substantially plate shape along a predetermined direction, and a second end surface formed on the same plane including the first end surface The first and second magnetic cores are wound around the second magnetic core and the core portion integrated at the end opposite to the first and second end faces. The permanent magnet is disposed in proximity to the side surface opposite to the second magnetic core of the first magnetic core.

  According to such a metal detection device, a magnetic flux is generated between the magnetic pole of the permanent magnet, the first end surface of the first magnetic core, and the second end surface of the second magnetic core integrated with the first magnetic core. As a result, the permanent magnet is disposed close to the side surface of the first magnetic core, so that the magnetic field gradient along the direction perpendicular to the predetermined direction of the magnetic flux density on the front surfaces of the first and second end surfaces is large. Is set. When an object to be inspected such as a metal piece moves across the front of the first end face and the front of the second end face, the spatial distribution of magnetic flux between the permanent magnet and the first and second magnetic cores is large. Turbulence occurs, a temporal fluctuation occurs in the density of the magnetic flux passing from the permanent magnet through the second magnetic core, and the inspection object is detected by detecting the fluctuation of the magnetic flux density by the coil wound around the second magnetic core. . At this time, by providing the permanent magnet having the above-described configuration and the core portion including the first and second magnetic cores, the fluctuation value of the magnetic flux density is increased, and the detection sensitivity can be effectively improved.

  The core portion has a substantially plate shape along a predetermined direction, a third end surface is formed on the same plane including the first and second end surfaces, and the third end surface is symmetric with the first magnetic core. It is preferable to further have a third magnetic core integrated with the second magnetic core at the end opposite to the end face of the first magnetic core. In this case, since the magnetic field gradient can be set over a wide range between the first to third magnetic cores and the magnetic poles of the permanent magnet, the detection sensitivity of the detection object can be further improved.

  Moreover, it is also preferable that the core part is formed of a high magnetic permeability material. If such a core portion is provided, the magnetic flux density in the region passing from the permanent magnet to the core portion is increased, and the spatial change in the magnetic flux density from the front surface of the first end surface to the front surface of the second end surface is further increased. The detection sensitivity can be further improved.

  Furthermore, it is also preferable that the first magnetic core and the second magnetic core have a long shape extending in a direction perpendicular to a predetermined direction. By adopting such a configuration, dispersion of magnetic flux in a direction perpendicular to the predetermined direction can be suppressed, and a spatial change in magnetic flux density from the front surface of the first end surface to the front surface of the second end surface is increased. Therefore, the detection sensitivity can be further improved.

  Furthermore, it is preferable that the end portion of the magnetic pole of the permanent magnet is located substantially on the same plane as the first and second end surfaces. In this way, the magnetic flux density in the space near the permanent magnet and the core portion can be maximized, and the detection sensitivity can be further improved.

  According to the present invention, the detection sensitivity can be improved regardless of the shape of the metal to be detected, and the number of parts can be reduced.

  Hereinafter, a preferred embodiment of a metal detection device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  1 is a perspective view showing an internal configuration of a metal detection device 1 according to a preferred embodiment of the present invention, FIG. 2 is a plan view of the metal detection device 1 of FIG. 1, and FIG. 3 is a metal detection of FIG. 2 is a front view of the device 1. FIG. The metal detection device 1 is a device that detects a magnetic piece (inspected object) such as a metal piece contained in an object to be detected such as food or electronic parts, and a coil wound around the core 2 and the core 2. 3 and a permanent magnet 4 provided close to the core portion 2 and a detection circuit portion 5 connected to both ends of the coil 3. Here, in each figure, the extending direction of the core portion 2 is the Y-axis direction, the direction perpendicular to the Y-axis and the side surface of the core portion 2 is the X-axis direction, and the direction perpendicular to the X-axis and the Y-axis is the Z-axis. The direction (predetermined direction) is assumed.

  The core part 2 is constituted by three magnetic cores 2a, 2b, 2c having a substantially rectangular plate shape so as to have a plane parallel to the YZ plane, and these magnetic cores 2a, 2b, 2c are on the bottom face 6 side of the core part 2. As a result, the cross section along the ZX plane is substantially E-shaped. The magnetic cores 2a, 2b, 2c have substantially the same width in the Y-axis and Z-axis directions. The core portion 2 has an elongated shape along the Y-axis direction, and the end surface 7a extends along the same plane parallel to the XY plane at the end in the + Z-axis direction of each of the magnetic cores 2a, 2b, 2c. , 7b, 7c are formed. That is, the core portion 2 is formed with end faces 7a, 7b, 7c that are discontinuous with each other on a plane parallel to the XY plane at one end in the Z-axis direction, and is opposite to the end faces 7a, 7b, 7c. At the other end portion on the side, the magnetic cores 2a, 2b, 2c are integrated along a plane parallel to the XY plane.

  As a material for such a core portion 2, silicon steel, which is a magnetic material having a relatively high magnetic permeability and a relatively large saturation magnetic flux density, is more preferably used. (Iron-aluminum-silicon alloy), low nickel permalloy or the like which is an iron-nickel alloy having a nickel content of 50% or less is also used.

  A coil 3 is wound around the central magnetic core 2b of the three magnetic cores 2a, 2b, 2c of the core portion 2 along the XY plane. A detection circuit unit 5 that detects a change in the voltage across the coil 3 is connected to both ends of the coil 3, and the time change of the voltage across the terminal based on the induced electromotive force generated in the coil 3 by the detection circuit unit 5. Is detected, and the detection result is output to an external device connected to the detection circuit unit 5. As such a detection circuit unit 5, a voltage amplification circuit including a feedback amplifier or the like is used.

  The permanent magnet 4 is a sintered magnet such as a rectangular parallelepiped neodymium magnet, close to the central portion in the Y-axis direction of the outer side surface 8 opposite to the magnetic core 2c of the magnetic core 2a, and its upper surface 9 is the magnetic core 2a. , 2b, 2c are arranged so as to be on the same plane as the end faces 7a, 7b, 7c. The permanent magnet 4 has both magnetic poles on the top surface 9 and the bottom surface 10, and both magnetic poles located on the top surface 9 and the bottom surface 10 are disposed along the Z-axis direction.

  In the metal detection device 1 having such a configuration, a transport path A that transports the detection target object is provided along the X-axis direction in front of the central portion in the longitudinal direction of the core portion 2 in the + Z-axis direction. Yes. When the object to be detected is transported to such a transport path A, a time change occurs in the voltage at both ends of the coil 3 due to the magnetic piece included in the object to be detected, and the time change is detected by the detection circuit unit 5. Is done.

  Next, the principle of detection of an inspection object by the metal detection device 1 will be described.

  FIG. 4 shows a distribution of magnetic flux generated between the core portion 2 and the permanent magnet 4 when the magnetic piece B included in the detection target object moves along the transport path A. As shown in FIG. 4A, some of the lines of magnetic force extending along the Z-axis from the upper surface 9 of the permanent magnet 4 are bent toward the end surfaces 7a, 7b, and 7c of the core portion 2 in front of the upper surface 9. Mostly, the magnetic cores 2a, 2b and 2c penetrate through the cores 2a, 2b and 2c along the Z axis through the end faces 7a, 7b and 7c of the magnetic cores 2a, 2b and 2c having high permeability.

  Here, when the magnetic piece B moves along the transport path A from the front of the upper surface 9 of the permanent magnet 4 toward the front of the end surface 7a of the magnetic core 2a, the magnetic flux distribution in front of the upper surface 9 is disturbed, and the magnetic core 2c. The magnetic flux distribution changes so that a part of the magnetic flux penetrating through the end face 7b of the magnetic core 2b changes (FIG. 4A). As a result, the magnetic flux penetrating the inside of the coil 3 increases, resulting in a time change in the voltage across the coil 3.

  On the other hand, when the magnetic piece B moves along the transport path A from the front of the end surface 7b of the magnetic core 2b toward the front of the end surface 7c of the magnetic core 2c, the magnetic flux distribution in front of the end surface 7b is disturbed and penetrates the magnetic core 2b. It changes so that a part of magnetic flux may penetrate the end surface 7c of the magnetic core 2c (FIG.4 (b)). As a result, the magnetic flux penetrating the inside of the coil 3 is reduced, and a time change occurs in the voltage across the coil 3.

  According to the metal detection device 1 described above, magnetic flux is generated between the magnetic poles of the permanent magnet 4 and the end faces 7a, 7b, 7c of the magnetic cores 2a, 2b, 2c, and the permanent magnet 4 is disposed close to the side surface of the magnetic core 2a. As a result, the magnetic flux distribution along the X-axis direction of the magnetic flux density on the front surfaces of the end faces 7a, 7b, and 7c becomes asymmetric, and as a result, the magnetic field gradient in the X-axis direction is set large. This is because by using the magnetic cores 2a, 2b, 2c made of a high permeability material, most of the magnetic flux emitted from the permanent magnet 4 is focused on the end faces 7a, 7b, 7c of the respective magnetic cores 2a, 2b, 2c. Due to that. When the magnetic piece B moves across the front of the end faces 7a and 7b, a large spatial disturbance occurs in the magnetic flux distribution between the permanent magnet 4 and the magnetic cores 2a, 2b and 2c, and the magnetic core 2b is moved from the permanent magnet 4 to the magnetic core 2b. A temporal variation occurs in the density of the magnetic flux passing therethrough, and the magnetic piece B is detected by detecting the variation in the magnetic flux density by the coil 3 wound around the magnetic core 2b. In general, in the case of detecting a magnetic piece such as a metal piece that generates only weak magnetism, inserting a core of a high magnetic permeability material into a detection coil is not This has led to a decrease in sensitivity due to the magnetic field. In the present embodiment, by arranging the permanent magnet 4 and the core portion 2 having a predetermined shape close to each other, the fluctuation value of the magnetic flux density is increased, and the detection sensitivity of the magnetic piece can be effectively improved.

  Further, by providing the magnetic core 2b around which the coil 3 is wound with the magnetic core 2a of the core portion 2 interposed between the permanent magnet 4 and the magnetic saturation of the coil 3 can be prevented. Can be reliably improved.

  Furthermore, since the core part 2 has a long shape, dispersion of magnetic flux in the Y-axis direction can be suppressed, and a spatial change in magnetic flux density over the front surfaces of the end faces 7a, 7b, and 7c can be increased. Therefore, the detection sensitivity can be further improved.

  Further, since the upper surface 9 (the end portion of the magnetic pole) of the permanent magnet 4 is located on substantially the same plane as the end surfaces 7a, 7b, 7c, the magnetic flux density in the space near the permanent magnet 4 and the core portion 2 is maximized. And detection sensitivity can be further improved.

  In addition, this invention is not limited to embodiment mentioned above. For example, various deformation | transformation aspects can be taken as a shape of the core part 2, and you may be comprised only by the magnetic cores 2a and 2b (FIG. 5). Moreover, the shape of each surface, such as end surface 7a, 7b, 7c of the core part 2, side surface 8, and bottom face 6, is not limited to a plane, A curved surface may be sufficient. Moreover, a permanent magnet may be arrange | positioned also at the side surface side of the magnetic core 2c.

It is a perspective view which shows the internal structure of the metal detection apparatus 1 concerning suitable one Embodiment of this invention. It is a top view of the metal detection apparatus of FIG. It is a front view of the metal detection apparatus of FIG. It is a front view which shows distribution of the magnetic flux which generate | occur | produces between the core part and permanent magnet of FIG. 1 when a to-be-detected target object moves along a conveyance path. It is a front view of the metal detection apparatus which shows the modification of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal detection apparatus, 2 ... Core part, 3 ... Coil, 2a, 2b, 2c ... Magnetic core, 7a, 7b, 7c ... End face, 4 ... Permanent magnet, 5 ... Detection circuit part, 8 ... Side surface.

Claims (5)

Permanent magnets arranged such that the magnetic poles are positioned along a predetermined direction;
A first magnetic core formed with a first end surface substantially perpendicular to the predetermined direction along the predetermined direction, and a substantially plate shape along the predetermined direction. And having a second magnetic core having a second end surface formed on the same plane including the first end surface, wherein the first and second magnetic cores are the first and second end surfaces. An integrated core at the opposite end;
A coil wound around the second magnetic core,
The permanent magnet is disposed in proximity to a side surface of the first magnetic core opposite to the second magnetic core,
A metal detector characterized by the above. The core portion has a substantially plate shape along the predetermined direction, a third end surface is formed on the same plane including the first and second end surfaces, and is symmetric with the first magnetic core. And further having a third magnetic core integrated with the second magnetic core at the end opposite to the third end face,
The metal detection device according to claim 1. The core portion is formed of a high permeability material.
The metal detection device according to claim 1, wherein the metal detection device is a metal detector. The first magnetic core and the second magnetic core are elongated so as to extend in a direction perpendicular to the predetermined direction.
The metal detection device according to claim 1, wherein the metal detection device is a metal detector. The end of the magnetic pole of the permanent magnet is located on substantially the same plane as the first and second end faces.
The metal detection device according to claim 1, wherein the metal detection device is a metal detector.

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