JP2008218729A - Magnetic shield box for metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic shield box for a metal detector which can efficiently reduce invasion of magnetic noise from an opening for transporting an inspection target object thereinto or therefrom. <P>SOLUTION: An inner-wall extension duct 87 and an outer-wall extension duct 88 are provided to be extended outwardly of inner and outer walls of an opening 81 of a magnetic shield box 80 for a metal detector respectively. In this embodiment, the inner-wall extension duct 87 is provided as a feature. Even when the outer-wall extension duct 88 is not necessarily provided, the inner-wall extension duct 87 enables efficient magnetic shielding from external magnetism to a certain level. The inner-wall extension duct 87 and a permalloy layer 83 outside of the outer wall are provided not to be contacted with each other with a gap therebetween. Even when the outer-wall extension duct 88 is provided, the outer-wall extension duct 88 is not overlapped with the inner-wall extension duct 87. Since the provision of the outer-wall extension duct 88 provides a higher shielding effect, it is desirable to provide the both ducts. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic shield box for a metal detector, and more particularly to a magnetic shield box for a metal detector in which an overhanging duct is provided at an opening.

  Conventionally, in order to ensure the safety of products, particularly foods, it is important to detect metallic foreign substances in the products, and the development of detection methods and devices has been underway. Generally, an induction coil type magnetic detection device as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 7-198860) has been widely used.

  However, depending on the detection target, it is difficult to set the dip phase angle and sensitivity of the magnetic detection device, and in order to increase detection accuracy, two magnetic detection devices are used to pass the inspection target at different angles. There has been a demand for a magnetic detection device with higher accuracy.

On the other hand, the superconducting material has characteristics such as Josephson effect and magnetic flux quantization. Using these properties, a superconducting quantum interference device (SQUID: Superductive Quantum Interference Device), which is a highly sensitive magnetic sensor, is manufactured. Therefore, the inventor of the present application has developed a superconducting metal detection apparatus for meat disclosed in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-151064) to meet this demand, and the meat It has been put to practical use as a metal detection device not only for food but also for general products from food.
JP-A-7-198860 JP 2004-151064 A

  Even in general products, for example, a minute metal foreign matter mixed in a lithium-ion battery for a personal computer may cause a fire accident, and even an industrial product may detect a minute metal foreign matter. It has become a big issue. In industrial use, a smaller metal becomes a problem than in food use. Therefore, it is necessary to detect foreign matter of 100 micrometers or less with high sensitivity.

  When performing detection with high sensitivity, in general, an object to be inspected that has been mixed with foreign matter is magnetized (magnetized) with a strong magnet, and then high-sensitivity magnetism such as a superconducting quantum interference device (SQUID) is used. A method of measuring the residual magnetization of a metal foreign object in an object to be inspected using a sensor is performed. In this case, since the magnetic sensor is highly sensitive, there is a problem that noise is mixed in by the geomagnetism or the magnetic field from the peripheral device, and the signal to be measured is buried in the noise. Therefore, a magnetic shield box that is generally double or triple made of a high magnetic permeability material called permalloy is made, and a sensor is housed therein to inspect foreign matter. As a result, intrusion of magnetic noise from the outside can be prevented.

  FIG. 5 is a schematic perspective view of a conventional superconducting metal detector, and FIG. 6 is a schematic cross-sectional view of a magnetic shield of the conventional superconducting metal detector. A superconducting metal detection device 1 shown in FIG. 5 includes a superconducting quantum interference device 10 for magnetic detection, a cooling device 20, a magnetic shield 30, a conveyor 40, an exclusion mechanism 46, a magnetizing device 50, A control unit 70 and a frame 78 are provided. The magnetic shield 30 has a two-layer structure of a permalloy layer 34 which is a high magnetic permeability material, and an opening 31 serving as an entrance / exit of the conveyor 40 is provided at the front and rear.

  The magnetic shield is made of a magnetic shielding material, and an amorphous alloy or the like is used as the magnetic shielding material. However, a permalloy magnetic shield is often used from the viewpoint of function and cost. However, permalloy magnetic shields are still expensive and this cost reduction is desired.

  In the superconducting metal detector 1 shown in FIGS. 5 and 6, openings 31 serving as entrances and exits of the conveyor 40 are provided on the front and back wall surfaces of the magnetic shield 30. Since an external magnetic field leaks from the opening 31 to the inside of the shield 30 and the shielding performance deteriorates, there is a problem that a sufficiently large magnetic shielding effect cannot be obtained. As a countermeasure, a method of reducing a leakage magnetic field from the opening by installing a cylindrical (rectangular or cylindrical) duct in the opening has been devised. In the prior art, a structure in which a duct is provided outward from the shield has been generally performed.

  An object of the present invention is to provide a magnetic shield box for a metal detector that can efficiently reduce the intrusion of magnetic noise from the entrance / exit of an inspection object.

Magnetic shield box for metal detector of the present invention,
A magnetic shield box that is attached to a metal detection device that detects magnetism and detects metal remaining inside an object to be inspected, and shields the internal magnetic sensor from external magnetic noise. A hollow box body disposed so as to have a gap between the inner wall, first and second openings provided in each of the outer wall and the inner wall, and a first opening provided in the second opening; And an inner wall projecting duct projecting toward the opening.

  A gap may be provided between the front end of the inner wall projecting duct and the inner side surface of the outer wall, and an outer wall projecting duct that projects from the first opening of the outer wall toward the outside of the outer wall may be provided. It is desirable that the inner surface of the outer wall overhanging duct and the outer surface of the inner wall overhanging duct do not overlap, and the overhanging length from the outer wall surface of the outer wall overhanging duct is shorter than the square root of the multiplier of the height and width of the opening. Preferably, the wall member forming the outer wall and the inner wall may be a permalloy layer or a combination of a permalloy layer and an aluminum layer and / or a steel plate layer.

  At the opening of the magnetic shield box for metal detectors, an inner wall projecting duct made of magnetic shielding material is provided at least from the inner wall to the outer wall, and a gap is provided between the tip of the inner wall projecting duct and the inside of the outer wall surface. Since the inner surface of the outer wall projecting duct and the outer surface of the inner wall projecting duct are configured not to overlap each other, the influence of magnetic noise from the outside entering through the opening is efficiently suppressed.

  The present invention provides a projecting duct made of a magnetic shielding material from the inner wall surface to the outer wall surface of the wall portion at the opening portion of the magnetic shield box for the metal detector without contacting the outer wall surface, and the opening portion of the wall surface. Since it is provided so as not to overlap with the projecting duct projecting outward from the outside, there is an effect that it is possible to efficiently suppress the influence of magnetic noise from the outside entering through the opening.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a magnetic shield box for a metal detector according to an embodiment of the present invention. The magnetic shield box 80 for metal detector is used as an alternative to the magnetic shield 30 of the superconducting metal detector 1 described with reference to FIGS. 5 and 6 in the section “Problems to be Solved by the Invention”.

  The magnetic shield box for metal detector 80 is configured in a hexahedral box shape having a double wall structure of an inner wall and an outer wall, and an opening 81 for carrying in / out an inspection object of the metal detector is provided on both sides facing each other. Have. The opening 81 includes a first opening 81a provided on the outer wall and a second opening 81b provided on the inner wall. Here, since the inspection object is carried in and out by the conveyor, openings are provided on both sides, but for example, when installing the inspection object at the inspection position by hand or tool, only one side may be used. This embodiment can also be applied. Openings 81 are provided in the respective inner and outer walls.

  In this embodiment, the inner wall is composed of an inner permalloy layer 82, and the outer wall is composed of an outer permalloy layer 83 provided with the space portion 84 sandwiched from the inner wall. It has a two-layer structure. The thickness of each plate and the width of the space are determined in accordance with the size of the metal detector magnetic shield box 80. Further, as will be described in the application examples described later, the magnetic shielding material is not limited to permalloy.

  An inner wall projecting duct 87 and an outer wall projecting duct 88 are provided outward from the second opening 81b on the inner wall and the first opening 81a on the outer wall of the metal detector magnetic shield box 80, respectively. There is an example in which only the outer wall projecting duct is provided in the conventional magnetic shield box, but the present embodiment is characterized in that the inner wall projecting duct 87 is provided. Even if the outer projecting duct 88 is not necessarily provided, the inner projecting duct 87 provides a certain degree of magnetic shielding from the outside.

  The inner wall overhanging duct 87 and the inner surface of the permalloy layer 83 on the outer wall are not in contact with each other, and a gap is provided therebetween. Even when the outer wall projecting duct 88 is provided, the inner wall projecting duct 87 and the outer wall projecting duct 88 do not overlap each other.

  2A and 2B are shape diagrams of a simulation model of an overhanging duct of a magnetic shield box for a metal detector according to an embodiment of the present invention. FIG. 2A is a front sectional view, FIG. 2B is a side sectional view, and FIG. It is a graph which shows the result.

  A simulation model shown in FIG. 2 and a simulation model having no overhang were produced, and the shielding degree was measured by changing the length of the overhang duct. The result is the graph shown in FIG. Here, the shielding degree is shield external magnetic density / internal magnetic flux density.

  As can be seen from the graph shown in FIG. 3, the degree of shielding is improved even with only the outer layer duct as compared with the case without the duct, but the degree of shielding is less increased even if the duct length is increased. The inner layer duct alone has a higher degree of shielding than the outer layer duct alone, but in the case of this model, the overhang length is rather lowered when it is more than about half of the interval between the inner and outer walls. In this case, the maximum distance between the inner wall and the outer wall of the duct is 80 mm, and the duct length is 40 mm. Therefore, it can be seen that the shielding effect is small even when extending to the outer wall or overlapping the outer layer duct. Since the shielding effect of the inner layer duct that does not protrude to the outside is greater than the shielding effect of the outer layer duct that protrudes to the outside, it is only necessary to determine whether to provide only the inner layer duct or the outer layer duct in relation to the entire apparatus. If both the inner layer duct and the outer layer duct are provided, the shielding effect is further increased as shown in FIG.

  In the conventional magnetic shield 30 composed of the two permalloy layers 34 of the outer wall 33 and the inner wall 32 in FIG. 6, the magnetic material to be measured and the high-sensitivity magnetic sensor are in the vicinity of the opening 31. Although the influence of the magnetic noise generated from the environment input via the opening 31 on the magnetic sensor could not be excluded, in the present embodiment, the inner wall extending duct 87 communicating with the inside of the shield box is provided as the second. The degree of shielding could be improved by providing the opening 81b.

  According to the calculated value using the model, as shown in FIG. 3, the extension length of the outer wall extension duct is about ½ of the height of the opening, and the shielding degree is about 1. Although it was tripled, there was almost no change in the degree of shielding even if it was made longer. Therefore, a proportional effect cannot be obtained by simply increasing the length of the outer wall projecting duct. According to the simulation results, the shielding effect does not increase even if the height is longer than the square root of the multiplier of the height and width of the opening.

  The magnetic shield box for metal detector 80 of the present embodiment has an effect of effectively shielding noise due to electromagnetic waves generated by, for example, a mobile phone, in addition to noise mixed by geomagnetism and magnetic fields from peripheral devices.

  An application example using a configuration of a magnetic shielding material different from the embodiment described so far will be described. FIG. 4 is a schematic sectional view of an application example of the magnetic shield box for a metal detector according to the embodiment of the present invention.

  In the embodiment of FIG. 1, only two permalloy layers are used as the magnetic shielding material of the magnetic shield box for the metal detector. However, in the application example of FIG. 4, the inner permalloy layer is used in the magnetic shield box 90 for the metal detector. A three-layer composite structure is provided in which an aluminum layer 93 is provided on the inner side of 92 with a first space 95 therebetween. An aluminum layer 93 is provided on the bottom surface so as to be at the same position as the upper side of the opening 91, and the aluminum layer 93 surrounds the internal superconducting quantum interference device 10, the cooling device 20, and the heat insulating container 21. Yes.

  As a result of simulations assuming a model for comparison with a conventional permalloy two-layer structure, in a three-layer composite structure model including an aluminum layer with high conductivity, the eddy current is increased as the frequency of magnetic noise increases. The magnetic shielding effect was increased, and the shielding degree was greatly increased against high frequency noise.

  Since the configuration of the overhanging duct of the application example is the same as that of the embodiment of FIG. 1, description of the structure and effects of the overhanging duct is omitted.

It is a typical sectional view of the magnetic shield box for metal detectors of an embodiment of the invention. It is a shape figure of the model for simulation of the overhanging duct of the magnetic shield box for metal detectors of embodiment of this invention, (a) is front sectional drawing, (b) is side sectional drawing. It is a graph which shows the result of simulation. It is typical sectional drawing of the example of application of the magnetic shield box for metal detectors of embodiment of this invention. It is a typical perspective view of the conventional superconductivity type metal detector. It is typical sectional drawing of the magnetic shield of the conventional superconducting type metal detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Superconducting type metal detection apparatus 10 Superconducting quantum interference element 20 Cooling device 30 Magnetic shield 31, 81 Opening part 32 Inner wall part 33 Outer wall part 34 Permalloy layer 40 Conveyor 46 Exclusion mechanism 50 Magnetizing device 70 Control part 78 Frame 80, 90 Metal Magnetic shield box for detector 81, 91 opening 81a first opening 81b second opening 82 inner permalloy layer 83 outer permalloy layer 84 space 87, 97 inner wall extending duct 88, 98 outer wall extending duct 92 inner Permalloy layer 93 Aluminum layer 94 Outer permalloy layer 95 First space 96 Second space

Claims (6)

A magnetic shield box that is attached to a metal detection device that detects magnetism and detects metal remaining inside the inspection object, and shields the internal magnetic sensor from external magnetic noise,
A hollow box body arranged such that the outer wall and the inner wall have a gap;
First and second openings provided in each of the outer wall and the inner wall;
A magnetic shield box for a metal detector, comprising: an inner wall projecting duct provided at the second opening and projecting toward the first opening. The magnetic shield box for a metal detector according to claim 1,
A magnetic shield box for a metal detector, wherein a gap is provided between a tip of the inner wall projecting duct and an inner surface of the outer wall. In the magnetic shield box for a metal detector according to claim 1 or 2,
A magnetic shield box for a metal detector, comprising an outer wall projecting duct projecting from the first opening of the outer wall toward the outside of the outer wall. In the magnetic shield box for a metal detector according to claim 3,
A magnetic shield box for a metal detector, wherein an inner surface of the outer wall projecting duct and an outer surface of the inner wall projecting duct do not overlap. In the magnetic shield box for a metal detector according to claim 3 or 4,
The length of the outer wall projecting duct extending from the outer wall surface is shorter than the square root of the multiplier of the height and width of the opening. The magnetic shield box for a metal detector according to claim 1,
A magnetic shield box for a metal detector, wherein the wall member forming the outer wall and the inner wall is a permalloy layer or a combination of a permalloy layer and an aluminum layer and / or a steel plate layer.

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