JP2009092507A - Magnetic material detecting device and magnetic material detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic material detecting device detecting magnetic materials highly precisely by reducing an influence of environmental magnetic noise with a simple and inexpensive device configuration. <P>SOLUTION: The magnetic material detecting device 100 comprises: a magnetizing device 20 for magnetizing a magnetic foreign matter, mixed in an inspected body 1, in a predetermined direction; a detecting section 10 to detect the magnetic foreign matter; a control equipment 30; and a conveying mechanism 40 for conveying the inspected body 1. The detecting section 10 comprises a magnetic sensor 18 disposed within a magnetic shield 12. The magnetic sensor 18 is a SQUID gradiometer having a pair of detecting coils with differential configuration. The magnetic sensor 18 is disposed so that coil face of the detecting coils has a predetermined angle to a moving face of the inspected body 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic substance detection device and a magnetic substance detection method for nondestructively detecting a magnetic substance mixed in an object to be inspected, and more specifically to a configuration using a superconducting quantum interference element (SQUID).

  In a production line for products such as foods, foreign matters such as metal strips derived from raw materials and metal fragments due to damaged wear of production equipment in the production process may be mixed in by mistake. Therefore, conventionally, the safety of a product has been ensured by detecting foreign matter mixed in the product before product shipment and eliminating the foreign matter-mixed product.

  Conventionally, X-ray foreign matter inspection devices using X-rays or metal detection devices using overcurrent have been applied as methods for detecting foreign matter in such products, but there is a problem that detection accuracy is low. there were.

  Therefore, recently, in order to solve such problems, a magnetic foreign object is detected using a magnetic sensor using a superconducting quantum interference device (SQUID) (hereinafter also referred to as “SQUID”). A configuration has been proposed (see, for example, Patent Document 1).

The SQUID is an element having a Josephson junction that applies a so-called tunnel effect in which an insulator is inserted in a superconducting ring. In order to make the SQUID function as a magnetic sensor, a bias current slightly exceeding the critical current value of the Josephson junction is applied to the element. The output voltage of the SQUID changes according to the magnetic field from the outside, and a minute magnetic field from the outside can be detected by detecting this voltage change.
JP 2005-351804 A

  However, as described above, when a SQUID is used to detect a magnetic foreign substance in a product, there is a problem that environmental magnetic noise generated in a production line or the like is erroneously detected because of high magnetic sensitivity. It was. Therefore, conventionally, a configuration has been adopted in which environmental magnetic noise is shielded by providing a magnetic shield and disposing a SQUID therein. However, since this magnetic shield is generally made of a highly permeable material such as permalloy, the cost and size of the apparatus are increased, causing a problem in versatility.

  The present invention has been made to solve such problems, and its object is to detect magnetic substances with high accuracy by reducing the influence of environmental magnetic noise with a simple and inexpensive apparatus configuration. And a magnetic substance detection device.

  Another object of the present invention is to provide a magnetic substance detection method capable of detecting a magnetic substance with high accuracy by reducing the influence of environmental magnetic noise with a simple and inexpensive apparatus configuration.

  According to one aspect of the present invention, when a magnetic material is mixed in an object to be inspected, a magnetic material detecting device for detecting the magnetic material, the magnetic device for magnetizing the magnetic material in a predetermined direction And a magnetic material based on a current corresponding to a difference in magnetic flux interlinked with each of the two detection coils, the coil surface being a surface that receives a magnetic field being arranged on the same plane. And a transport mechanism that moves at least one of the inspection object and the magnetic sensor so that the relative position of the inspection object and the magnetic sensor changes. The magnetic sensor is arranged such that the coil surfaces of the two detection coils have a predetermined angle with respect to a plane perpendicular to the predetermined direction.

  According to another aspect of the present invention, there is provided a magnetic substance detection method for detecting a magnetic substance using a magnetic sensor when a magnetic substance is mixed in an object to be inspected. The coil surface which is a receiving surface has two detection coils arranged on the same plane. The magnetic substance detection method includes magnetizing a magnetic substance in a predetermined direction, arranging the coil surfaces of the two detection coils so as to have a predetermined angle with respect to a plane perpendicular to the predetermined direction, According to the step of moving at least one of the inspection object and the magnetic sensor so that the relative position between the inspection object and the magnetic sensor changes, and the difference in magnetic flux linked to each of the two detection coils Detecting a magnetic substance based on the current.

  According to the magnetic substance detection device and the magnetic substance detection method described above, by arranging the magnetic sensor so that the coil surfaces of the two detection coils have a predetermined angle with respect to a plane perpendicular to the magnetization direction of the magnetic substance, Even when the distance between the object to be inspected and the detection coil exceeds the distance between the centers of the detection coils, the magnetic substance can be detected with high detection accuracy while reducing the influence of environmental magnetic noise.

  According to another aspect of the present invention, when a magnetic material is mixed in an object to be inspected, the magnetic material detection device detects the magnetic material, and the coil surface that receives the magnetic field is on the same plane. A magnetic sensor for detecting a magnetic substance based on a current corresponding to a difference in magnetic flux linked to each of the two detection coils, an object to be inspected, and a magnetic sensor And a transport mechanism for moving at least one of the object to be inspected and the magnetic sensor so that the relative position of the sensor changes. The magnetic sensor is arranged so that the coil surfaces of the two detection coils have a predetermined angle with respect to the relative movement surface of the object to be inspected.

  According to another aspect of the present invention, there is provided a magnetic substance detection method for detecting a magnetic substance using a magnetic sensor when a magnetic substance is mixed in an object to be inspected. The coil surface which is a surface which receives a magnetic field has two detection coils arranged on the same plane. In the magnetic substance detection method, the step of moving at least one of the inspection object and the magnetic sensor so that the relative position between the inspection object and the magnetic sensor changes, and the coil surfaces of the two detection coils are inspected. A step of disposing a predetermined angle with respect to a relative movement surface of the body, and a step of detecting a magnetic substance based on a current corresponding to a difference in magnetic flux linked to each of the two detection coils. With.

  According to the magnetic substance detection device and the magnetic substance detection method described above, by arranging the magnetic sensor so that the coil surfaces of the two detection coils have a predetermined angle with respect to the relative movement surface of the object to be inspected, Even when the distance between the detection coil and the object to be inspected exceeds the distance between the centers of the detection coils, it is possible to detect a magnetic substance with high detection accuracy while reducing the influence of environmental magnetic noise.

Preferably, the predetermined angle is less than 90 degrees.
More preferably, the predetermined angle is approximately 45 degrees.

  According to the magnetic substance detection device described above, a significant difference is generated in the magnetic flux interlinked with each of the two detection coils, and the magnetic field sensing direction of the magnetic sensor is not orthogonal to the magnetization direction of the magnetic substance. The detection sensitivity of the magnetic sensor can be ensured.

  Preferably, the predetermined angle is set according to a relative distance between the magnetic sensor and the object to be inspected.

  Preferably, the magnetic substance detection method further includes a step of setting a predetermined angle according to a relative distance between the magnetic sensor and the object to be inspected.

  According to the above magnetic substance detection device and magnetic substance detection method, the detection sensitivity of the magnetic sensor can be stably ensured regardless of the relative distance between the magnetic sensor and the object to be inspected.

  Preferably, the magnetic substance detection device further includes a shield member for shielding magnetic noise from the outside.

  According to the above magnetic substance detection device, since the influence of environmental magnetic noise can be reduced, it is possible to construct a magnetic substance detection device using a shield member that is smaller and less expensive than conventional magnetic substance detection devices. it can.

Preferably, the magnetic sensor is a gradiometer.
According to the above magnetic substance detection device, the magnetic substance can be detected with high detection accuracy while reducing the influence of environmental magnetic noise by using a gradiometer including a plurality of detection coils.

  According to the present invention, the influence of environmental magnetic noise can be reduced with a simple and inexpensive apparatus configuration. As a result, it is possible to detect the magnetic substance with high accuracy.

  Embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals and description thereof will not be repeated.

(overall structure)
FIG. 1 is a schematic configuration diagram of a magnetic substance detection device 100 according to an embodiment of the present invention.

  Referring to FIG. 1, a magnetic substance detection device 100 according to an embodiment of the present invention is typically used for detection of magnetic foreign matter mistakenly mixed into a product in a product line. The magnetic foreign matter can be detected by inducing a magnetic moment of the magnetic foreign matter mixed in the object to be inspected and detecting this with a magnetic sensor.

  More specifically, the magnetic substance detection device 100 includes a detection unit 10, a magnetism device 20, a control device 30, and a transport mechanism 40.

  The detection unit 10 includes a magnetic shield 12 made of a highly permeable material such as permalloy, a magnetic sensor 18 disposed in the magnetic shield 12, and a support base 11 that supports the magnetic shield 12.

  The magnetic shield 12 has openings 120 a and 120 b on the front and rear sides along the transport direction of the transport path 42. The device under test 1 placed on the belt 44 of the transport path 42 is introduced into the magnetic shield 12 space through the openings 120a and 120b.

  The magnetic shield 12 shields geomagnetism and environmental magnetic noise to prevent adverse effects on the magnetic detection operation. By disposing the magnetic shield 12, magnetic foreign matter can be detected even in a general environment such as a product line. The magnetic shield 12 can be formed of a plurality of layers depending on the environment. A radio wave shield is also provided if necessary.

  The magnetic sensor 18 is configured using a superconducting quantum interference device (SQUID) (hereinafter also referred to as “SQUID”). The SQUID is an element having a Josephson junction that applies a so-called tunnel effect in which an insulator is inserted in a superconducting ring. The magnetic sensor 18 is cooled within the magnetic shield 12 to maintain the SQUID in a superconducting state. Specifically, the magnetic sensor 18 is immersed in the cooling medium 16 stored in the container portion 14.

  The SQUID may be composed of either a low-temperature superconductor made of niobium compound or the like, or a high-temperature superconductor made of ceramics. However, in the magnetic substance detection apparatus 100 according to the present embodiment, the high-temperature superconductor is made of The case of using will be described. Since the high-temperature superconductor enters a superconducting state at about 90 K, liquid nitrogen (boiling point: 77.3 K) is used as the cooling medium 16. In addition, when using a low-temperature superconductor, it is necessary to use liquid helium (boiling point: 4.2K) as a cooling medium.

  The container portion 14 is typically made of a nonmagnetic material such as glass epoxy, and a vacuum layer (not shown) is formed on the outer periphery of the container portion 14 in order to suppress heat intrusion from the outside of the container. Moreover, the container part 14 is sealed with the cover part (not shown) for preventing heat penetration.

  The magnetism device 20 is disposed in the vicinity of the opening 120 a on the entrance side of the magnetic shield 12. The magnetism device 20 includes a pair of permanent magnets 22 and 24 arranged in the vertical direction with the conveyance path 42 interposed therebetween. In addition, as long as it produces | generates a strong magnetic field, not only a permanent magnet but an electromagnet may be sufficient.

  When the device under test 1 passes through the magnetism device 20, the pair of permanent magnets 22 and 24 applies a DC magnetic field to the magnetic foreign matter present in the device under test 1. As a result, the magnetic foreign matter is forcibly magnetized so as to have a magnetic field H that is perpendicular to the conveyance direction of the object 1 to be inspected, and is surely in a magnetized state. As a result, the detection sensitivity of the magnetic foreign matter in the magnetic sensor 18 can be improved. If the detection sensitivity of the magnetic sensor 18 is sufficiently high, the magnetism device 20 may not be provided.

  The transport mechanism 40 includes a transport path 42 for transporting the device under test 1 and a support base 50 that supports the transport path 42. The conveyance path 42 includes a belt 44 that conveys the device under test 1, a roller 48 that smoothly moves the belt 44, and a pulley 46 that is arranged before and after the conveyance direction to drive the belt 44. The belt 44 passes through the magnetic shield 12 and transports the device 1 to be inspected carried out from the magnetism device 20 into the magnetic shield 12, and also carries out the device 1 to be inspected after inspection from the magnetic shield 12.

FIG. 2 is a partial cross-sectional side view of detection unit 10 according to the embodiment of the present invention.
With reference to FIG. 2, the magnetic sensor 18 is disposed so as to face the conveyance path 42 at the bottom of the container portion 14. That is, the magnetic sensor 18 is disposed above the conveyance path 42 and detects the magnetic field H from the magnetic foreign object 2 of the object 1 to be inspected that moves along the conveyance path 42.

  The magnetic sensor 18 is coupled to a drive circuit (not shown) via a wiring 182 that is inserted and guided in a hollow insulating tube 180 having a small coefficient of thermal expansion. This drive circuit is provided in the control device 30.

  As shown in FIG. 2, when the magnetic sensor 18 is disposed at the bottom of the container portion 14 to bring the magnetic sensor 18 close to the object 1 to be inspected, the magnetic object 2 is included in the object 1 to be inspected. In addition, the magnetic field H caused by the magnetic foreign matter 2 can be detected with high accuracy.

(Magnetic sensor)
Here, the principle of magnetic field detection by the SQUID used for the magnetic sensor 18 will be described with reference to FIG.

  Referring to FIG. 3, SQUID 60 is made of a superconducting material formed in a loop shape, and two Josephson junctions JJ are formed on the loop. This Josephson junction JJ has a structure in which an insulating material is laminated with two superconducting materials, and its characteristics as a superconducting material are low as compared with other portions. Therefore, the Josephson junction JJ shifts from the superconducting state to the normal conducting state earliest in the SQUID 60. That is, when the current flowing through the loop exceeds a predetermined limit value, the SQUID 60 has a portion in the normal conduction state, but this limit value is limited by the Josephson junction JJ.

  By the way, SQUID60 produces the phenomenon (Meissner effect) which excludes the magnetic flux which penetrates self in a superconducting state. More specifically, when an external magnetic flux attempts to penetrate the SQUID 60, a shielding current for canceling the magnetic flux flows. It is possible to detect whether or not there is a magnetic flux that attempts to penetrate the SQUID 60 by the following method using the Meissner effect, and if so, the magnitude of the magnetic flux.

  First, a bias current substantially equal to a limit value at which the Josephson junction JJ can maintain the superconducting state is given from the outside. In this state, when the magnetic flux passes through the SQUID 60, a shielding current flows in a direction to cancel the magnetic flux. The Josephson junction JJ exceeds a limit value capable of maintaining a superconducting state when the shielding current flows, and the excess current becomes a normal conductive current and generates electric resistance. In this case, since the electric resistance varies according to the magnitude of the shielding current, that is, the magnitude of the magnetic flux, the magnitude of the magnetic flux penetrating the SQUID 60 is measured by measuring the output voltage caused by the electric resistance. Can be detected.

  And, as a magnetic sensor using this SQUID, typically, it has one detection coil, and is composed of a magnetometer that detects a magnetic field interlinking the detection coil, and a plurality of detection coils. There are two types of gradiometers that detect differences in interlinkage magnetic flux.

  FIG. 4 is a diagram for explaining a configuration using a magnetometer as the magnetic sensor 18.

  Referring to FIG. 4A, the inspection object 1 (not shown) mixed with the magnetic foreign material 2 moves along the transport direction (corresponding to the x-axis direction in the drawing). The magnetometer is arranged so that the coil surface, which is the surface that receives the magnetic field of SQUID 60, is parallel to the moving surface of the magnetic foreign material 2 (corresponding to the xy plane in the figure). That is, the magnetometer is arranged so that the z-axis direction is the magnetic field sensing direction, and the magnetic field sensing direction is coincident with the magnetization direction of the magnetic foreign material 2.

  The SQUID 60 outputs this sensitive magnetic flux in the form of a voltage by being driven using a known feedback circuit called FLL (Flux Locked Loop). The feedback magnetic flux is input to the SQUID 60 through the feedback coil 56.

  FIG. 4B is a diagram showing an output signal of the magnetometer when the magnetic foreign material 2 moves in the x-axis direction. The output signal of FIG. 4B is obtained by simulating the magnetic flux interlinking with the SQUID 60 in the configuration of FIG.

Referring to FIG. 4B, it can be seen that the output signal shows a sharp peak when the distance between the magnetic foreign object 2 and the SQUID 60 is the shortest. Here, the magnetic flux generated in the SQUID 60 is quantized in units of magnetic flux quantum φ ₀ (= 2.07 × 10 ⁻¹⁵ Wb). The FLL feedback circuit, since than flux quantum phi ₀ will be able to detect small magnetic flux, the magnetometer can detect small magnetic field 0.1~1pT level.

  On the other hand, due to such a high magnetic sensitivity, the magnetometer detects not only the magnetic field H of the magnetic foreign matter 2 but also the environmental magnetic noise generated from the surrounding magnetic noise sources. There is a possibility that the foreign object 2 is erroneously detected. Therefore, when the magnetic foreign object 2 is detected using a magnetometer, a magnetic shield having a high shielding rate against environmental magnetic noise is required. Therefore, when detecting the magnetic flux by the magnetic foreign material 2 using a magnetometer, in order to eliminate the influence of environmental magnetic noise, a large and expensive high shielding rate magnetic shield must be provided.

  On the other hand, as described below, in the case where a gradiometer composed of a plurality of detection coils is used for the magnetic sensor 18, the influence of environmental magnetic noise can be reduced, so that the above-described problems are avoided. Is possible.

  FIG. 5 is a diagram schematically showing a gradiometer. FIG. 6 is a plan view showing a configuration example of the gradiometer of FIG. 5 and 6 show, as an example, a primary differential type gradiometer including a pair of detection coils.

  Referring to FIG. 5, the gradiometer 70 has two detection coils 701 and 702 having substantially the same area and arranged in parallel. Differences in magnetic flux interlinking with the detection coils 701 and 702 are transmitted to the SQUID 60. The reason why the areas of the two detection coils 701 and 702 are substantially equal is to effectively cancel the environmental magnetic noise between the detection coils.

  That is, from the gradiometer 70, an output voltage proportional to the spatial gradient of the magnetic flux density linked to the two detection coils 701 and 702 is obtained. At this time, the environmental magnetic noise having a magnetic noise source at a location distant from the detection coils 701 and 702 has a substantially zero difference because the magnetic fluxes linked to the detection coils 701 and 702 are substantially equal. As a result, the influence of environmental magnetic noise can be eliminated from the output (detected magnetic field) of the gradiometer 70.

  Even when the gradiometer 70 is used for the magnetic sensor 18, it is preferable to provide a magnetic shield in order to detect the magnetic flux due to the magnetic foreign substance 2 with higher accuracy. However, this magnetic shield can be constructed with a small and inexpensive one compared to the case of using a magnetometer.

  Referring to FIG. 6, gradiometer 70 includes a substrate 72 and a superconducting thin film pattern 74 formed on substrate 72. In the superconducting thin film pattern 74, two detection coils 701 and 702 which are superconducting thin film loops are formed symmetrically. The detection coils 701 and 702 having a rectangular shape share one side, and a SQUID 60 is formed at the center of the one side.

  More specifically, the SQUID 60 has an opening at the central portion, and a Josephson junction 76 is formed at two predetermined portions located on the right side of the SQUID 60 with the opening interposed therebetween. For example, the Josephson junction 76 is formed by utilizing weak coupling formed on the stepped portion by covering the stepped portion provided on the substrate 72 with a superconductive material. Two terminals 78 are connected to the left and right ends of the SQUID 60 across the Josephson junction 76 via terminal connection portions 77, respectively.

  In the configuration of FIG. 6, when receiving a magnetic flux from the outside, the detection coils 701 and 702 flow shield currents I1 and I2 corresponding to the number of linkages, respectively. Therefore, when the detection coil 701 has a larger number of flux linkages than the detection coil 702, the shielding current I1 is larger than the shielding current I2. Then, when the difference in the shield current (= I1−I2) flows through the SQUID 60, the difference in magnetic flux interlinking with the detection coils 701 and 702 is detected.

  Next, the detection operation of the magnetic foreign matter 2 in the magnetic substance detection apparatus 100 using the gradiometer 70 having the above configuration as the magnetic sensor 18 will be described.

  FIG. 7 is a diagram for explaining a configuration using a gradiometer 70 as the magnetic sensor 18.

  Referring to FIG. 7A, the inspection object 1 (not shown) mixed with the magnetic foreign material 2 moves along the transport direction (corresponding to the x-axis direction in the drawing). The gradiometer 70 is arranged so that the coil surfaces of the detection coils 701 and 702 are parallel to the moving surface of the magnetic foreign material 2 (corresponding to the xy plane in the drawing). That is, the gradiometer 70 is arranged so that the z-axis direction is the magnetic field sensing direction, and the magnetic field sensing direction matches the magnetization direction of the magnetic foreign material 2.

  As described above, the detection coils 701 and 702 share one side, and two Josephson junctions 76 are formed on the one side.

  In such a configuration, when the magnetic foreign object 2 moves along the x-axis direction, the distances L1 and L2 between the magnetic foreign object 2 and the detection coils 701 and 702 change continuously. And according to the change of this distance L1, L2, the magnetic flux linked to the detection coils 701, 702 changes continuously. At this time, an output signal proportional to the difference between the magnetic fluxes linked to the detection coils 701 and 702 is obtained from the gradiometer 70.

  FIG. 7B is a diagram showing an output signal of the gradiometer 70 when the magnetic foreign material 2 moves in the x-axis direction.

  Referring to FIG. 7B, it can be seen that the output signal has peaks on the positive side and the negative side, respectively. The positive peak indicates that the magnetic flux interlinking with the detection coil 701 is larger than the magnetic flux interlinking with the detection coil 702, and the negative peak indicates that the magnetic flux interlinking with the detection coil 702 is chained with the detection coil 701. It shows that there are more magnetic fluxes that intersect. These peaks are caused by a continuous change in the magnitude relationship between the distances L1 and L2 between the detection coils 701 and 702 and the magnetic foreign matter 2 as the magnetic foreign matter 2 moves.

  Further, in the output signal, the peak has a magnitude proportional to the difference between the magnetic fluxes linked to the detection coils 701 and 702, respectively. The larger this peak, the higher the detection accuracy.

  However, due to the configuration of the magnetic substance detection device 100, the distances L1 and L2 between the detection coils 701 and 702 and the magnetic foreign object 2 may be sufficiently longer than the base line LT which is the distance between the centers of the detection coils 701 and 702. is there. In this case, since the distance L1 and the distance L2 are substantially equal, the magnetic fluxes linked to the detection coils 701 and 702 are substantially equal. As a result, the peak of the output signal becomes small, and it is difficult to accurately detect the magnetic foreign material 2.

  In such a case, in order to increase the detection accuracy, it is effective to make the baseline LT longer. However, since there is no large single crystal substrate on which a superconducting thin film is formed, it is not always easy to form a large-area superconducting thin film pattern 74 (FIG. 5).

  Therefore, as means for providing a significant difference in the distances L1 and L2 to the magnetic foreign object 2 between the detection coils 701 and 702 without changing the baseline LT, as shown in FIG. It can be considered that the gradiometer 70 is arranged (hereinafter also referred to as a vertical arrangement) so that the coil surface is perpendicular to the moving surface (xy plane) of the magnetic foreign matter 2.

  FIG. 8 is a diagram for explaining a configuration in which the gradiometer 70 as the magnetic sensor 18 is vertically arranged.

  Referring to FIG. 8A, the inspection object 1 (not shown) mixed with the magnetic foreign material 2 moves along the transport direction (corresponding to the x-axis direction in the drawing). The gradiometer 70 is arranged such that the coil surfaces of the detection coils 701 and 702 are perpendicular to the moving surface of the magnetic foreign material 2 (corresponding to the xy plane in the drawing). That is, the gradiometer 70 is arranged so that the x-axis direction is the magnetic field sensing direction, and the magnetic field sensing direction is orthogonal to the magnetization direction of the magnetic foreign material 2.

  In such a configuration, when the magnetic foreign object 2 moves along the x-axis direction, the distances L1 and L2 between the magnetic foreign object 2 and the detection coils 701 and 702 change continuously. As the distances L1 and L2 change, the magnetic fluxes linked to the detection coils 701 and 702 change continuously. At this time, an output signal proportional to the difference between the magnetic fluxes linked to the detection coils 701 and 702 is obtained from the gradiometer 70.

  FIG. 8B is a diagram illustrating a simulation result of the output signal of the gradiometer 70 when the magnetic foreign material 2 moves in the x-axis direction.

  Referring to FIG. 8B, the output signal has a peak on each of the positive side and the negative side. It can be seen that the size of each peak is larger than the peak of the output signal shown in FIG. This is because the base line LT of the detection coils 701 and 702 is directly the difference between the distances L1 and L2 to the magnetic foreign object 2. Assuming that the peak size of the output signal of the magnetometer shown in FIG. 4B is 1, the result of the simulation is about 0.13.

  On the other hand, the output signal indicates zero at a position where the magnetic foreign object 2 is closest to the detection coils 701 and 702, that is, a position where the magnetic foreign object 2 is directly below the detection coils 701 and 702. The reason why the output signal becomes zero at the position where the magnetic foreign matter 2 is directly below the detection coils 701 and 702 is that the magnetization direction (x-axis direction) of the magnetic foreign matter 2 is the magnetic field of the gradiometer 70 immediately below the detection coils 701 and 702. This is because the magnetic field H of the magnetic foreign material 2 cannot be detected because it is orthogonal to the sensing direction (z-axis direction).

  In this way, when the coil surfaces of the detection coils 701 and 702 are arranged perpendicular to the moving surface of the magnetic foreign object 2, the coil surfaces are arranged in parallel to the moving surface of the magnetic foreign material 2. Thus, while the level of the output signal at the peak can be increased, the output signal shows a peak at a position offset from the position immediately below the detection coils 701 and 702. Since the distance from the offset position to the detection coils 701 and 702 is longer than the distance from the position immediately below the detection coils 701 and 702 to the detection coils 701 and 702, the detection sensitivity of the magnetic field H is disadvantageous. turn into. Therefore, in order to ensure detection sensitivity, it is required that the output signal exhibits a peak at a position closer to the position immediately below the detection coils 701 and 702.

  Therefore, in the magnetic substance detection device according to the present embodiment, the gradiometer 70 is arranged so that the coil surfaces of the detection coils 701 and 702 have a predetermined angle with respect to the moving surface of the magnetic foreign object 2 (hereinafter referred to as an inclined arrangement). Also referred to as). The predetermined angle is set to an angle smaller than 90 °. Hereinafter, as an example, the detection operation when the predetermined angle is 45 ° will be described.

  FIG. 9 is a diagram for explaining a configuration in which the gradiometer 70 as the magnetic sensor 18 is disposed in an inclined manner.

  Referring to FIG. 9A, the inspected object 1 (not shown) mixed with the magnetic foreign material 2 moves along the transport direction (corresponding to the x-axis direction in the figure). The gradiometer 70 is arranged such that the coil surfaces of the detection coils 701 and 702 have an angle of 45 ° with respect to the moving surface of the magnetic foreign matter 2 (corresponding to the xy plane in the drawing). That is, the gradiometer 70 is arranged so that the direction inclined by 45 ° with respect to the z-axis direction is the magnetic field sensing direction.

  In such a configuration, when the magnetic foreign object 2 is conveyed along the x-axis direction, the distances L1 and L2 between the magnetic foreign object 2 and the detection coils 701 and 702 change continuously. As the distances L1 and L2 change, the magnetic fluxes linked to the detection coils 701 and 702 change continuously. At this time, an output signal proportional to the difference between the magnetic fluxes linked to the detection coils 701 and 702 is obtained from the gradiometer 70.

  FIG. 9B is a diagram showing a simulation result of the output signal of the gradiometer 70 when the magnetic foreign material 2 moves in the x-axis direction.

  Referring to FIG. 9B, the output signal has peaks on the positive side and the negative side, respectively. It can be seen that the size of each peak is larger than the peak of the output signal shown in FIG. Assuming that the magnitude of the peak of the output signal of the magnetometer shown in FIG. 4B is 1, the result of the simulation is about 0.22.

  Further, the output signal shows a peak at a position substantially directly below the central portion of the detection coils 701 and 702.

  As described above, the coil surfaces of the detection coils 701 and 702 are inclined with respect to the moving surface of the magnetic foreign matter 2, so that the output signal peaks at a position substantially directly below the central portion of the detection coils 701 and 702. As shown, the peak size is larger than the vertical arrangement.

  Even at this position, in addition to the significant difference in the distances L1 and L2 from the magnetic foreign material 2 to the detection coils 701 and 702 due to the baseline LT, the magnetization direction of the magnetic foreign material 2 and the gradiometer 70 are also different. This is because the detection sensitivity of the gradiometer 70 is ensured because the magnetic field sensing direction is not orthogonal.

As a result, by arranging the gradiometer 70 to be inclined with respect to the moving surface of the magnetic foreign matter 2, it is possible to detect the magnetic foreign matter 2 with high detection sensitivity while reducing the influence of environmental magnetic noise.
(Actual measurement data)
FIG. 10 shows that when a magnetometer (FIG. 4) is used as the magnetic sensor 18, a gradiometer (FIG. 6) is used as the magnetic sensor 18, and the coil surfaces of the detection coils 701 and 702 are moved with respect to the moving surface of the magnetic foreign matter 2. When the gradiometer 70 is arranged so as to be vertical, and a gradiometer is used as the magnetic sensor 18, the coil surfaces of the detection coils 701 and 702 have an angle of 45 ° with respect to the moving surface of the magnetic foreign matter 2. It is a figure which shows the actual measurement result in the case where the gradiometer 70 is arranged as described above.

  The actual measurement result is shown in FIG. 1 under the condition that the detection coils 701 and 702 of the gradiometer 70 have the same shape as the detection coil of the magnetometer and the base line is the same as the length of one side of the detection coil. 2 and 2 are obtained respectively when the inspection object 1 is transported.

  Referring to FIG. 10, line LN <b> 1 indicates the output signal of the magnetometer, and line LN <b> 2 indicates the output of the gradiometer arranged so that the coil surface of the detection coil is perpendicular to the moving surface of magnetic foreign matter 2. The line LN3 indicates the output signal of the gradiometer that is inclined so that the coil surface of the detection coil has an angle of 45 ° with respect to the moving surface of the magnetic foreign object 2.

  Comparing the peak signal level among these three output signals, the output signal of the magnetometer is the largest, and the output of the gradiometer inclined so as to have an angle of 45 ° with respect to the moving surface of the magnetic foreign matter 2 The output signal of the gradiometer arranged next to the next largest signal and perpendicular to the moving surface of the magnetic foreign material 2 is the smallest. Specifically, when the peak of the output signal of the magnetometer is 1, the output signal of the gradiometer arranged vertically is about 0.17 while the peak of the output signal of the gradiometer arranged vertically is about 0.17. The signal peak was about 0.25. These indicate that the simulation results shown in FIG. 8 and FIG. 9 are verified.

  From the above results, it was shown that the detection sensitivity is ensured because the peak of the output signal can be increased while the gradiometer 70 is arranged vertically by being inclined.

  In addition, regarding the predetermined angle formed by the coil surfaces of the detection coils 701 and 702 and the moving surface of the magnetic foreign substance 2 in the inclined arrangement of the gradiometer 70, the baseline LT of the gradiometer 70, the gradiometer 70, and the device under test 1 Can be appropriately adjusted so that the magnetic sensitivity is optimized. For example, the predetermined angle may be made variable according to the distance between the gradiometer 70 and the device under test 1.

(Example of change)
In addition, the effect in this Embodiment mentioned above can be acquired also by arrange | positioning the conveyance path 42 inclining with respect to the gradiometer 70, as shown in FIG. That is, as long as the coil surfaces of the detection coils 701 and 702 and the moving surface of the magnetic foreign substance 2 have a predetermined angle, either the conveyance path 42 or the gradiometer 70 may be inclined.

  Furthermore, since the relative positions of the detection coils 701 and 702 and the magnetic foreign material 2 only need to change continuously, the magnetic sensor 18 can be moved instead of the magnetic foreign material 2.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic block diagram of the magnetic substance detection apparatus according to embodiment of this invention. It is a partial cross section side view of the detection part according to embodiment of this invention. It is a figure for demonstrating the principle of the magnetic field detection by SQUID. It is a figure for demonstrating the structure which used the magnetometer as a magnetic sensor. It is a figure which shows a gradiometer typically. It is a top view which shows the example of 1 structure of the gradiometer of FIG. It is a figure for demonstrating the structure which used the gradiometer as a magnetic sensor. It is a figure for demonstrating the structure which has arrange | positioned the gradiometer vertically. It is a figure for demonstrating the structure which inclinedly arranged the gradiometer. It is a figure which shows the actual measurement result in a magnetometer and a gradiometer. It is a schematic block diagram of the magnetic substance detection apparatus according to the modification of embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Test object, 2 Magnetic foreign material, 10 Detection part, 11, 50 Support stand, 12 Magnetic shield, 14 Container part, 16 Cooling medium, 18 Magnetic sensor, 20 Magnetic band device, 22, 24 Permanent magnet, 30 Control apparatus, 40 Conveyance mechanism, 42 Conveyance path, 44 Belt, 46 Pulley, 48 rollers, 701, 702 Detection coil, 56 Feedback coil, 60 SQUID, 70 Gradiometer, 72 Substrate, 74 Superconducting thin film pattern, 76 Josephson junction, 77 terminals Connection part, 78 terminals, 100 magnetic substance detection device, 120a, 120b opening, 180 cavity tube, 182 wiring, JJ Josephson coupling.

Claims (10)

When a magnetic substance is mixed in an object to be inspected, a magnetic substance detection device that detects the magnetic substance,
A magnetic device for magnetizing the magnetic material in a predetermined direction;
The magnetic material has two detection coils arranged on the same plane as a surface for receiving a magnetic field, and the magnetic material is based on a current corresponding to a difference in magnetic flux linked to each of the two detection coils. A magnetic sensor for detecting
A transport mechanism that moves at least one of the inspection object and the magnetic sensor so that a relative position between the inspection object and the magnetic sensor changes;
The magnetic sensor is a magnetic substance detection device in which coil surfaces of the two detection coils are arranged so as to have a predetermined angle with respect to a plane perpendicular to the predetermined direction. When a magnetic substance is mixed in an object to be inspected, a magnetic substance detection device that detects the magnetic substance,
The magnetic material has two detection coils arranged on the same plane as a surface for receiving a magnetic field, and the magnetic material is based on a current corresponding to a difference in magnetic flux linked to each of the two detection coils. A magnetic sensor for detecting
A transport mechanism that moves at least one of the inspection object and the magnetic sensor so that a relative position between the inspection object and the magnetic sensor changes;
The magnetic sensor is a magnetic substance detection device in which coil surfaces of the two detection coils are arranged so as to have a predetermined angle with respect to a relative movement surface of the object to be inspected.   The magnetic substance detection apparatus according to claim 1, wherein the predetermined angle is less than 90 degrees.   The magnetic substance detection apparatus according to claim 3, wherein the predetermined angle is approximately 45 degrees.   The magnetic object detection device according to claim 3, wherein the predetermined angle is set according to a relative distance between the magnetic sensor and the inspection object.   The magnetic substance detection device according to claim 1, further comprising a shield member for shielding magnetic noise from the outside.   The magnetic substance detection apparatus according to claim 1, wherein the magnetic sensor is a gradiometer. A magnetic substance detection method for detecting a magnetic substance using a magnetic sensor when a magnetic substance is mixed in an object to be inspected,
The magnetic sensor has two detection coils in which coil surfaces, which are surfaces that receive a magnetic field, are arranged on the same plane,
The magnetic substance detection method includes:
Magnetizing the magnetic material in a predetermined direction;
Arranging the coil surfaces of the two detection coils to have a predetermined angle with respect to a surface perpendicular to the predetermined direction;
Moving at least one of the inspection object and the magnetic sensor so that a relative position between the inspection object and the magnetic sensor changes;
Detecting the magnetic material based on a current corresponding to a difference in magnetic flux interlinking with each of the two detection coils. A magnetic substance detection method for detecting a magnetic substance using a magnetic sensor when a magnetic substance is mixed in an object to be inspected,
The magnetic sensor has two detection coils in which coil surfaces, which are surfaces that receive a magnetic field, are arranged on the same plane,
The magnetic substance detection method includes:
Moving at least one of the inspection object and the magnetic sensor so that a relative position between the inspection object and the magnetic sensor changes;
Arranging the coil surfaces of the two detection coils so as to have a predetermined angle with respect to a relative movement surface of the object to be inspected;
Detecting the magnetic material based on a current corresponding to a difference in magnetic flux interlinking with each of the two detection coils.   The magnetic substance detection method according to claim 8, further comprising a step of setting the predetermined angle according to a relative distance between the magnetic sensor and the object to be inspected.

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