JP2012154675A - Metal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detector capable of stably and highly sensitively detecting a minute metal included in an inspection object with influence of disturbance noise eliminated.SOLUTION: A metal detector comprises: a magnetizing part 30 for magnetizing a metal m included in an inspection object W; a detection head 40 that includes a plurality of magnetic sensors 41a to 41c and 42a to 42c having sharp directivity along an orthogonal direction orthogonal to a conveyance direction of the inspection object W and arranged along the orthogonal direction, and for detecting a residual magnetic component of the metal m included in the inspection object W magnetized by the magnetizing part 30; a magnetic shield 49 disposed in the orthogonal direction of the detection head 40 so as to surround a part of a conveyance path for blocking noise entering the inside of the detection head 40; and projections 81 projecting from the surface of the inner wall of the magnetic shield 49 toward the magnetic sensors 41a to 41c and 42a to 42c in the vicinity of the plurality of magnetic sensors 41a to 41c and 42a to 42c arranged in lines.

Description

  The present invention relates to a metal detection device that detects the presence or absence of a metal in a test object such as food.

  Conventionally, as this type of metal detection device, a metal detection device that detects the presence or absence of metal in an object to be inspected, such as food, based on a change in magnetic field generated by the passage of the object to be inspected, a plurality of detection sensors in the transport direction And at least one of the plurality of detection sensors is provided via a conveyance path, and a combined detection signal when the object to be inspected is not conveyed. There is known a technique in which the noise level included in the detection signal is reduced by setting the connection state between the detection sensors so that the signal level is minimized (see, for example, Patent Document 1).

In addition, a large number of fluxgate magnetic detection elements are arranged on the document placement surface on which a document can be placed, and whether or not staples are attached to the document is determined based on the detection signal of each fluxgate magnetic detection element. What is determined by sensitivity is known (for example, see Patent Document 2).
JP 2005-227029 A JP 2006-189376 A

  However, in the conventional metal detection device, although the noise level can be reduced to a certain extent by the technique of Patent Document 1, the sensitivity is limited due to the influence of disturbance noise.

  Further, in the technique of Patent Document 2, since there is no magnetizing device for magnetizing the metal in the inspection object, the detection sensitivity is not sufficient, and since no magnetic shield is provided, it is affected by disturbance noise. Therefore, there is a problem that a metal having a diameter of 1 mm or less cannot be detected.

  Therefore, the present invention has been made to solve the above-described conventional problems, and can eliminate the influence of disturbance noise and stably detect a minute metal in an object to be inspected with high sensitivity. An object of the present invention is to provide a metal detection device that can be used.

  The metal detection apparatus according to the present invention includes a transport unit that transports an object to be inspected in a transport path, a magnetizing unit that magnetizes metal in the test object transported by the transport unit, and a transport of the test object. A magnetic sensor having a sharp directivity in an orthogonal direction perpendicular to the direction and having a plurality of magnetic sensors arranged in the orthogonal direction, and detecting a residual magnetic component of a metal in an inspection object magnetized by the magnetizing means. A detection head, shielding means arranged in the orthogonal direction of the detection head so as to surround a part of the conveyance path, and shielding noise entering the inside of the detection head; and a plurality of the magnetic sensors arranged Judgment for determining the presence or absence of metal in the object to be inspected based on projections projecting from the surface of the inner wall of the shielding means toward the magnetic sensor and detection signals from a plurality of magnetic sensors of the detection head. Characterized by comprising a stage, a.

  With this configuration, a projection that protrudes from the surface of the inner wall of the shielding unit toward the magnetic sensor is provided on the inner wall of the shielding unit in the vicinity of the plurality of arranged magnetic sensors. Therefore, the influence of disturbance noise can be eliminated, and minute metals in the inspection object can be detected with high sensitivity.

  Further, the metal detection device according to the present invention is characterized in that the width of the protrusion is substantially the same as the width of the magnetic sensor in the orthogonal direction orthogonal to the conveyance direction of the inspection object.

  With this configuration, the magnetic lines of force caused by the magnetized metal can be efficiently collected near the magnetic sensor.

  In the metal detection device according to the present invention, the protrusions are in a line shape extending in at least one of a conveyance direction of the inspection object or a direction orthogonal to the conveyance direction.

  With this configuration, the magnetic lines of force caused by the magnetized metal can be efficiently collected near the magnetic sensor.

  Moreover, the metal detection apparatus according to the present invention is characterized in that the protrusion has a conical shape or a circular columnar shape with a round tip.

  With this configuration, the magnetic lines of force caused by the magnetized metal can be efficiently collected near the magnetic sensor.

  In the metal detection device according to the present invention, the magnetic sensor includes a core that provides an elongated magnetic path with respect to a magnetic field to be measured, and a detection coil wound around the core, and the magnetic moment of the core is It is characterized by comprising an orthogonal fluxgate sensor for supplying an alternating current to the core so as to be directed in an orthogonal direction periodically with respect to the longitudinal direction of the core.

  With this configuration, since the orthogonal fluxgate sensor is used as the magnetic sensor, it is possible to reduce the size and weight and to prevent the magnetic sensor itself from generating noise due to external vibration.

  The present invention can provide a metal detection device that can eliminate the influence of disturbance noise and can stably detect a minute metal in an inspection object with high sensitivity.

It is a perspective view of the metal detection apparatus which concerns on embodiment of this invention. (A) is a top view of the metal detection apparatus which concerns on embodiment of this invention, (b) is CC 'sectional drawing of (a), (c) is D of (a). It is -D 'sectional drawing. It is a circuit block diagram of the magnetic sensor of the metal detector which concerns on embodiment of this invention. (A), (b) is a figure which shows an example of the detection coil part of a magnetic sensor. It is a figure which shows the detection signal from the magnetic sensor of the metal detection apparatus which concerns on embodiment of this invention. It is sectional drawing which shows the case where the magnetic sensor of the metal detection apparatus which concerns on embodiment of this invention is arrange | positioned with a predetermined angle inclination with respect to the sequence direction. It is sectional drawing which shows the structure which provided the processus | protrusion in the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention. It is sectional drawing which shows the structure which provided the processus | protrusion on the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention, and has arrange | positioned two magnetic sensors in inclination. (A), (b) is sectional drawing which shows an example of the shape of the processus | protrusion of the inner wall of a magnetic shield. It is a perspective view which shows the structure which each provided the protrusion which became independent on the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention. It is a perspective view which shows the structure which provided the row | line | column-shaped protrusion extended in the conveyance direction of the to-be-inspected object W in the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention. It is a perspective view which shows the structure which provided the row | line | column-shaped protrusion extended in the direction orthogonal to the conveyance direction of the to-be-inspected object W in the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention. The structure which provided the row | line | column-shaped protrusion extended in both the conveyance direction of the to-be-inspected object W, and the direction orthogonal to a conveyance direction on the inner wall of the magnetic shield of the metal detector which concerns on embodiment of this invention in the grid | lattice form. FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the configuration will be described.

  As shown in FIGS. 1 and 2, the metal detection device 10 includes a conveyor 20 that conveys the inspection object W in the conveyance path 20 a, a magnetizing unit 30 that magnetizes the metal m in the inspection object W, and a target object. It has sharp directivity in an orthogonal direction (indicated by an arrow B) orthogonal to the conveyance direction of the inspection object W, and has a plurality of magnetic sensors 41 a to 41 e and 42 a to 42 e arranged in the orthogonal direction. A detection head 40 for detecting a component in the orthogonal direction of the remanent magnetism of the metal m in the magnetized workpiece W, and a noise that is disposed at both ends of the detection head 40 in the orthogonal direction and that enters the detection head 40 is detected. A magnetic shield 49 for shielding, and a determination means 53 for determining the presence or absence of the metal m in the object W based on detection signals from the plurality of magnetic sensors 41a to 41e and 42a to 42e of the detection head 40. Yes.

  The inspected object W is, for example, an arbitrary product packaged with a packaging material, such as a food container in a packaging container, and a label or tag for individual identification that can be magnetized on the surface of a rectangular parallelepiped packaging box. Etc. are attached or attached. The object W to be inspected is a metal foreign object or a magnetic printed matter printed with chemicals and magnetic ink in a packaging box.

  The conveyor 20 winds an endless belt 21 around a plurality of pairs of conveying rollers 22a, 22b, 23a, and 23b, and an object to be inspected from the entrance side to the exit side of the detection head 40 by the upper surface of the upper running portion of the belt 21. W is transported.

  A known magnetized portion 30 is installed at a predetermined position on the upstream side of the detection head 40 in the transport path 20a so as to face the top and bottom across the transport path 20a. The magnetized portion 30 includes a magnet (not shown) for applying a magnetic field in the vertical direction. Thus, the inspection object W is applied with a DC magnetic field by the magnetizing unit 30 at a position upstream of the magnetic detection region 45 so that the metal m in the inspection object W is magnetized at a predetermined residual magnetization level. It has become.

  The magnetizing unit 30 is provided to detect the metal m in the inspection object W with higher accuracy by the detection head 40, but is magnetized in advance outside the metal detection device 10. Thus, when the metal m in the inspection object W has magnetism sufficient for magnetic detection, the magnetized portion 30 does not need to be installed, and the apparatus configuration without the magnetized portion 30 can be obtained. .

  In addition, the orthogonal direction in which the plurality of magnetic sensors 41a to 41e and 42a to 42e are arranged is not strictly limited to 90 °, and is allowed as long as it is within the range not affected by noise. For example, the range is ± 30 °.

  The detection head 40 includes an upper head 41 and a lower head 42 that are arranged so as to face each other vertically with the conveyance path 20a of the inspection object W interposed therebetween. In the upper head 41, a plurality of magnetic sensors 41a to 41e are arranged in an orthogonal direction indicated by an arrow B orthogonal to the conveyance direction of the inspection object W. The lower head 42 is provided with a plurality of magnetic sensors 42 a to 42 e arranged in the orthogonal direction orthogonal to the conveyance direction of the inspection object W.

  A region sandwiched between the upper head 41 and the lower head 42 of the detection head 40 forms a magnetic detection region 45 through which the inspection object W conveyed in the direction of arrow A by the conveyor 20 passes.

  As shown in FIGS. 1 and 2A, magnetic shields 49 are provided at both ends of the detection head 40 in the orthogonal direction to shield noise entering the magnetic detection region 45 inside the detection head 40. In FIG. 1 and FIG. 2A, the magnetic shield 49 is wound to include both ends in the direction indicated by the arrow B (the width direction of the belt 21), which is a direction orthogonal to the conveyance direction of the inspection object W. Is provided so as to surround the conveyance path 20a.

  As shown in FIG. 2C, the magnetic sensors 41 a to 41 e and 42 a to 42 e are arranged in an in-plane direction (hereinafter also referred to as a sensitivity direction) orthogonal to the direction indicated by the arrow A that is the conveyance direction of the inspection object W. Has sharp directivity. For this reason, the magnetic sensors 41a to 41e and 42a to 42e can detect only the component in the orthogonal direction of the magnetic flux of the metal m in the inspection object W. In the present embodiment, the magnetic sensors 41a to 41e and 42a to 42e are composed of orthogonal flux gate sensors shown in FIG. By using orthogonal fluxgate sensors as the magnetic sensors 41a to 41e and 42a to 42e, it is possible to reduce the size and weight, and the magnetic sensors 41a to 41c and 42a to 42c themselves generate noise due to external vibration. This can be prevented. The magnetic sensors 41a to 41e and 42a to 42e are not limited to orthogonal fluxgate sensors, and may be any magnetic sensors that can have sharp directivity in a predetermined direction.

  Here, the fluxgate sensor is a small high-sensitivity sensor that can measure a magnetic field of 10 pT to a geomagnetic level in a frequency band from a static magnetic field to a low frequency without requiring cooling or heating. In a fluxgate sensor, a core that provides an elongated magnetic path for a magnetic field to be measured and a detection coil wound around the core are basic elements of the sensor head. There are two types of fluxgate sensors, ie, an orthogonal fluxgate sensor and a parallel fluxgate sensor, which differ in the method of periodically modulating the magnetic permeability of the core so that a static magnetic field can be measured. Among these, a type that is AC driven so that the magnetic moment of the core is orthogonal to the longitudinal direction of the core and modulates the magnetic permeability of the core is called an orthogonal fluxgate sensor. In the case of the orthogonal fluxgate sensor, since the magnetic permeability can be modulated by passing an alternating current directly through the magnetic wire, there is an advantage that the configuration of the sensor head can be simplified. In addition, by superimposing a DC current of about the amplitude value or more on the AC excitation current, the frequency of the signal voltage induced in the detection coil becomes the fundamental frequency of the excitation frequency (double frequency in the conventional fluxgate sensor), The circuit is simplified, sensitivity is increased, and core noise is suppressed. (Reference: Society of Electrical Engineers of Japan Magnetics: MAG-08-133 Operation and Characteristics of Fundamental Wave Type Orthogonal Flux Gate with Negative Feedback Configuration. Ichiro Hamada, Masanori Murakami (Kyushu University)) In this embodiment, output linearity In order to facilitate calibration of sensitivity and sensitivity, a method of adopting a negative feedback configuration for a fundamental wave type orthogonal fluxgate sensor using a U-shaped sensor head is adopted. The type that modulates the permeability by applying an AC magnetic field of several tens to several hundreds of kHz in the longitudinal direction of the core is called a parallel type flux gate sensor. In the parallel type flux gate sensor, the alternating current used for modulation is used. Since the excitation magnetic field and the magnetic field to be measured are parallel or antiparallel, it is usually configured to cancel the AC excitation magnetic field using two cores. The parallel fluxgate sensor requires an exciting coil for applying an alternating magnetic field.

  Further, the metal detection device 10 includes a control unit 50 having an AD conversion means 52, a determination means 53, and a result display means 54. Although a specific hardware configuration is not illustrated, the control unit 50 includes an EEPROM (Electronically Erasable and Programmable Read Only Memory), a hard disk, and the like as a nonvolatile memory in addition to a CPU, a ROM, a RAM, and an input / output interface circuit. In accordance with a predetermined metal detection control program stored in a ROM, EEPROM, hard disk or the like, a detection signal from the detection head 40, a threshold value for determination stored in a nonvolatile manner in the EEPROM, etc. It is determined whether or not the metal m is mixed in the inspection object W.

  The detection signals from the magnetic sensors 41a to 41e and 42a to 42e are respectively input to the AD conversion means 52 provided individually for the magnetic sensors 41a to 41e and 42a to 42e via the signal line 51. In addition, while the inspection object W passes through the magnetic detection region 45, the detection signals from the magnetic sensors 41a to 41e and 42a to 42e are converted from analog signals to digital signals by the AD conversion means 52, respectively. The determination means 53 provided individually for each of 41e and 42a to 42e refers to a determination threshold set in advance, and the presence or absence of metal is determined. The determination result by the determination unit 53 is displayed by the result display unit 54.

  The determination unit 53 not only determines the presence / absence of the metal m in the inspection object W based on the detection signals from the plurality of magnetic sensors 41a to 41e and 42a to 42e of the detection head 40, but also includes magnetic sensors 41a to 41e, By comparing the intensities of the detection signals from 42a to 42e, the position of the metal m in the inspection object W in the orthogonal direction indicated by the arrow B is calculated and output to the result display means 54.

  Furthermore, the determination means 53 is based on the difference (difference or ratio) in signal strength between the detection signals of the magnetic sensors 41a to 41e of the upper head 41 and the detection signals of the magnetic sensors 42a to 42e of the lower head 42. The position in the vertical direction indicated by the arrow H of the metal m in the inspection object W is calculated and output to the result display means 54.

  Hereinafter, specific configurations of the magnetic sensors 41a to 41e and 42a to 42e will be described. In addition, since the magnetic sensors 41a-41e and 42a-42e have the mutually same structure, the magnetic sensor 41a is demonstrated.

  As shown in FIG. 3, in the magnetic sensor 42a configured as an orthogonal fluxgate sensor, a coil that cancels the input magnetic field is provided as the detection coil 63, and the residual magnetic field is detected by the high sensitivity sensor. Is a negative feedback configuration that employs a zero position method that detects the magnitude of the input magnetic field from the magnitude of the current used to cancel the input magnetic field. In the negative feedback configuration employing the zero position method, there is an advantage that the linearity of the zero point portion is good and the dynamic range is widened.

  The sensor head 61 employs a U-shaped amorphous magnetic wire as the core 62, and one end of the detection coil 63 is grounded with a low resistance. In order to simplify the structure, the detection coil 63 is also used as a negative feedback coil. The exciting current of the core 62 is taken directly from the signal generator 64 having an output resistance of 50Ω for simplicity. Excitation applies a necessary DC bias voltage (Vdc) to a sine wave voltage (Vac) of 100 kHz. Since the detection voltage from the detection coil 63 is 100 kHz which is the same as the excitation frequency, it is input to the preamplifier 65 by AC coupling, and is demodulated in parallel by the synchronous detection circuit 66 and is then smoothed by a subsequent stage smoothing filter (cutoff frequency≈100 Hz). Conversion to direct current. The signal converted into direct current is amplified by a band-limited error amplifier 67 using 0 V as a reference voltage, and a negative feedback current for cancellation is superimposed on the detection winding via the high resistance Rf. Here, the reason why the resistance value of the high resistance Rf is increased is to convert the negative feedback current into a voltage with high sensitivity, and to prevent the feedback circuit from becoming a load when viewed from the detection coil 63. The selection of the time constant of the error amplifier on the input side and the negative feedback circuit side of the preamplifier 65 is set in the range of 1 / (C1R1)> 10 / (C2R2). The voltage across the high resistance Rf is extracted by a voltage follower (not shown) and then output through a subtraction circuit and a 60 Hz notch filter. As shown in FIG. 4A or FIG. 4B, the magnetic sensor 42a has an U-shaped core 62 made of amorphous wire, so that the left and right individual legs of the core 62 are independent of the input magnetic field. Thus, it is possible to prevent the occurrence of an offset by canceling the magnetic flux change generated in the magnetic field. Note that the length of the core 62 of the magnetic sensor 42a is optimally about 1.5 to 3 cm. This is because, if the core 62 is lengthened, the resolution can be increased and the directivity can be sharpened, while an insensitive body is generated at the center.

  Regarding the operation of the metal detection apparatus 10 described with reference to FIGS. 1 to 4, first, as shown in FIG. 5, when the inspection object W passes through the magnetic detection region 45, the magnetic sensors 41 a to 41 e and 42 a to 42- The detection signal from 42e is converted from an analog signal into a digital signal by the AD conversion means 52, and input to the determination means 53 provided individually for each of the magnetic sensors 41a to 41e and 42a to 42e.

  Assuming that the detection signals from the magnetic sensors 41a to 41e and 42a to 42e are the detection signals 41as to 41es and 42as to 42es, respectively, the determination unit 53 determines the threshold value for determination for each of the detection signals 41as to 41es and 42as to 42es. If there is a detection signal that exceeds the determination threshold value, a determination result indicating that the metal m is mixed is output to the result display means 54. Further, the determination means 53 determines that the metal m is mixed in the location of the magnetic sensor corresponding to the detection signal exceeding the determination threshold, and the orthogonality indicated by the arrow B of the metal m in the inspection object W. The position in the direction is calculated and output to the result display means 54. Further, the determination unit 53 determines that the metal m is mixed in the location of the magnetic sensor corresponding to the detection signal exceeding the determination threshold, and detects the detection signals 41as to 41a of the magnetic sensors 41a to 41e of the upper head 41. 41es and the detection signals 42as to 42es of the magnetic sensors 42a to 42e of the lower head 42 based on the difference (difference or ratio) in the vertical direction indicated by the arrow H of the metal m in the inspection object W. The position is calculated and output to the result display means 54. When receiving the determination result, the result display means 54 displays the presence / absence and position of the metal m in the inspection object W.

  As shown in FIG. 6, the magnetic shields 49 are disposed not only at both ends in the width direction of the belt 21 but also at both ends in the vertical direction (indicated by arrows H in FIGS. 1 and 2C). It is constructed integrally around the road. In this case, lines of magnetic force due to the magnetization of the metal m are attracted to the magnetic shield 49 at right angles in the vicinity of the magnetic shield 49. For this reason, when the magnetic sensors 41a to 41c and 42a to 42c and the magnetic shield 49 are arranged close to each other, the magnetic sensors 41a to 41c and 42a to 42c are arranged with respect to the arrangement direction of the magnetic sensors 41a to 41c and 42a to 42c, respectively. Sensitivity can be obtained by arranging 42c so as to be inclined by an angle α or −α. In FIG. 6, the arrangement direction of the magnetic sensors 41 a to 41 c and 42 a to 42 c is a straight line that substantially matches the width direction of the belt 21, but is not limited thereto.

  Further, in the metal detector 10, in order to further reduce the influence of disturbance noise and improve the S / N ratio, as shown in FIG. 7, the magnetic shield 49 in the vicinity of the magnetic sensors 41a to 41c and 42a to 42c is used. Protrusions 81 are preferably provided on the surface of the inner wall. In the following description, it is assumed that six magnetic sensors 41a to 41c and 42a to 42c are provided as in FIG. The protrusion 81 may have an integral structure in which the inner wall of the magnetic shield 49 is protruded inward, or is manufactured separately from the magnetic shield 49 by a material having the same characteristics as the magnetic shield 49. It may be fixed to the inner wall of the magnetic shield 49 above. In the example shown in FIG. 7, the protrusion 81 is formed integrally with the magnetic shield 49 and is formed by pressing the magnetic shield 49.

  As a result, as shown in FIG. 7, the magnetic lines of force caused by the magnetized metal m gather in the portion of the protrusion 81 of the magnetic shield 49, so that the density of the magnetic lines passing through the vicinity of the magnetic sensors 41 a to 41 c and 42 a to 42 c increases. Metal foreign matter can be detected with high sensitivity.

  Further, in the metal detection device 10, in order to increase the resolution, as shown in FIG. 8, the magnetic sensors 43 a to 43 f and 44 a to 44 f having the same configuration as the magnetic sensors 41 a to 41 c and 42 a to 42 c are replaced with the magnetic shield 49. It is preferable that the two magnetic sensors are disposed close to the inner wall at an angle of about 45 ° with respect to the inner wall of the magnetic shield 49 while being arranged to be inclined with respect to the inner wall. In this case, the magnetic sensors 43 a to 43 f and 44 a to 44 f are arranged to be inclined with respect to the inner wall of the magnetic shield 49, so that the magnetic sensors 43 a to 43 f and 44 a to 44 f come into contact with the belt 21 and the inner wall of the magnetic shield 49. Therefore, since the magnetic sensors 43a to 43f and 44a to 44f can be lengthened, the resolution can be increased. In FIG. 8, two magnetic sensors are disposed for one protrusion 81, but one magnetic sensor may be disposed for one protrusion 81.

  Hereinafter, a specific example of the shape and arrangement of the protrusion 81 will be described.

[Shape shape]
The shape of the protrusion 81 can be a conical shape with a sharp tip as shown in FIG. 9A, or a cylindrical shape with a rounded tip as shown in FIG. 9B.

  The width D2 of the protrusion 81 is preferably substantially the same as the width D1 of the magnetic sensors 41a to 41c and 42a to 42c in the orthogonal direction (sensitivity direction) orthogonal to the conveyance direction of the inspection object W. If the width D2 of the protrusion 81 is extremely smaller than the width D1 of the magnetic sensors 41a to 41c and 42a to 42c, the influence of concentrating the magnetic force lines on the protrusion 81 is reduced, while the width D2 of the protrusion 81 is less than the magnetic sensor 41a. This is because the density of magnetic lines passing through the vicinity of the magnetic sensors 41a to 41c and 42a to 42c corresponding to the protrusions 81 is reduced when the width D1 of .about.41c and 42a to 42c is extremely larger. By making the shape of the protrusion 81 into a conical shape with a sharp tip or a cylindrical shape with a rounded tip, and making the width D2 of the protrusion 81 substantially the same as the width D1 of the magnetic sensors 41a to 41c and 42a to 42c, The magnetic lines of force of the magnetized metal m can be efficiently collected in the vicinity of the magnetic sensors 41a to 41c and 42a to 42c.

  Note that the height of the protrusion 81 is preferably high enough not to contact the magnetic sensors 41a to 41c and 42a to 42c. That is, it is preferable that the space | interval of the front-end | tip of the processus | protrusion 81 and magnetic sensor 41a-41c, 42a-42c is narrow.

[Protrusion arrangement]
As for the arrangement of the protrusions 81, as shown in FIG. 10 which is a perspective view showing the lower half of the magnetic shield 49 configured as shown in FIG. 9, each of the protrusions 81 is independent on the surface of the inner wall of the magnetic shield 49 in the vicinity of the magnetic sensors 42a to 42c. In addition to providing the protrusions 81, as shown in FIG. 11, row-like protrusions 81 extending in the conveyance direction of the inspection object W may be provided. Also, as shown in FIG. 12, a row of protrusions 81 extending in a direction orthogonal to the direction of conveyance of the inspection object W is provided, or as shown in FIG. Row-shaped protrusions 81 extending in both directions perpendicular to the direction may be provided in a lattice shape. When configured as shown in FIGS. 11 to 13, the magnetic lines of force of the magnetized metal m can be efficiently collected in the vicinity of the magnetic sensors 41 a to 41 c and 42 a to 42 c.

  As described above, the metal detection device 10 according to the present embodiment includes the conveyor 20 that conveys the inspection object W, the magnetized portion 30 that magnetizes the metal m in the inspection object W, and the inspection object W. It has sharp directivity in the orthogonal direction (indicated by arrow B) orthogonal to the transport direction, and has a plurality of magnetic sensors 41 a to 41 c and 42 a to 42 c arranged in the orthogonal direction, and is magnetized by the magnetizing unit 30. The detection head 40 for detecting the residual magnetic component of the metal m in the object W to be inspected, and the detection head 40 arranged in a direction orthogonal to the detection head 40 so as to surround a part of the conveyance path, noise that enters the detection head 40 is detected. Protrusions projecting from the surface of the inner wall of the magnetic shield 49 toward the magnetic sensors 41a to 41c and 42a to 42c in the vicinity of the shielded magnetic shield 49 and the plurality of magnetic sensors 41a to 41c and 42a to 42c 1 and includes a plurality of magnetic sensors 41a~41c detection head 40, a determining unit 53 determines the presence or absence of metal m of the object in W based on the detection signal from 42 a to 42 c, a.

  With this configuration, in the vicinity of the plurality of magnetic sensors 41a to 41c and 42a to 42c, the protrusions 81 protruding from the inner wall surface of the magnetic shield 49 toward the magnetic sensors 41a to 41c and 42a to 42c are formed on the magnetic shield 49. Since it is provided on the inner wall, the magnetic lines of force of the magnetized metal m can be collected in the vicinity of the magnetic sensors 41a to 41c and 42a to 42c, and therefore, the influence of disturbance noise is eliminated, and the minute metal in the inspection object W is removed. m can be detected with high sensitivity.

  Further, in the metal detection device 10 according to the present embodiment, the width of the protrusion 81 is substantially the same as the width of the magnetic sensors 41a to 41c and 42a to 42c in the orthogonal direction orthogonal to the conveyance direction of the inspection object W. It is characterized by.

  With this configuration, the magnetic lines of force caused by the magnetized metal m can be efficiently collected near the magnetic sensors 41a to 41c and 42a to 42c.

  In addition, the metal detection device 10 according to the present embodiment is characterized in that the protrusions 81 are in a row extending in at least one of the conveyance direction of the inspection object W or the direction orthogonal to the conveyance direction.

  With this configuration, the magnetic lines of force caused by the magnetized metal m can be efficiently collected near the magnetic sensors 41a to 41c and 42a to 42c.

  Further, the metal detection device 10 according to the present embodiment is characterized in that the protrusion 81 has a conical shape or a circular columnar shape with a tip.

  With this configuration, the magnetic lines of force caused by the magnetized metal m can be efficiently collected near the magnetic sensors 41a to 41c and 42a to 42c.

  In addition, the metal detection device 10 according to the present embodiment includes a core 62 in which the magnetic sensors 41a to 41c and 42a to 42c provide an elongated magnetic path with respect to a magnetic field to be measured, and a detection coil wound around the core 62. 63, and an orthogonal flux for passing an alternating current and a direct current larger than the alternating current value to the core 62 such that the magnetic moment of the core 62 is periodically orthogonal to the longitudinal direction of the core 62. It consists of a gate sensor.

  With this configuration, since orthogonal flux gate sensors are used as the magnetic sensors 41a to 41c and 42a to 42c, the size and weight can be reduced, and the magnetic sensors 41a to 41c and 42a to 42c themselves vibrate from the outside. Therefore, noise can be prevented from being generated.

  The embodiment disclosed this time is illustrative in all respects and is not limited to this embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. For example, in the above embodiment, the shape of the protrusion is a conical shape or a cylindrical shape with a rounded tip. However, the shape is not limited to these shapes, and may be a shape such as a quadrangular prism.

  As described above, the metal detection device according to the present invention eliminates the influence of disturbance noise, has the effect of being able to stably detect a minute metal in an inspection object with high sensitivity, food, etc. It is useful as a metal detection device for detecting the presence or absence of metal in the inspection object.

10 Metal detection device 20 Conveyor (conveyance means)
21 Belt 30 Magnetized part (magnetizing means)
DESCRIPTION OF SYMBOLS 40 Detection head 41 Upper head 41a-41e, 42a-42e, 43a-43f, 44a-44f Magnetic sensor 42 Lower head 45 Magnetic detection area 49 Magnetic shield (shielding means)
DESCRIPTION OF SYMBOLS 50 Control part 51 Signal line 52 AD conversion means 53 Judgment means 54 Result display means 62 Core 63 Detection coil 64 Signal generator 65 Preamplifier 66 Synchronous detection part circuit 67 Error amplifier 81 Protrusion m Metal W Test object

Claims (5)

A transport means for transporting the inspection object in the transport path;
Magnetizing means for magnetizing the metal in the inspection object conveyed by the conveying means;
It has a sharp directivity in an orthogonal direction orthogonal to the conveyance direction of the inspection object, and has a plurality of magnetic sensors arranged in the orthogonal direction, and the metal in the inspection object magnetized by the magnetization means A detection head for detecting the residual magnetic component;
Shielding means arranged in the orthogonal direction of the detection head so as to surround a part of the transport path, and shielding noise entering the inside of the detection head;
In the vicinity of the plurality of magnetic sensors arranged, a protrusion protruding toward the magnetic sensor from the surface of the inner wall of the shielding means;
A metal detection apparatus comprising: determination means for determining presence or absence of metal in the inspection object based on detection signals from a plurality of magnetic sensors of the detection head.   The metal detection apparatus according to claim 1, wherein a width of the protrusion is substantially the same as a width in an orthogonal direction orthogonal to a conveyance direction of the inspection object in the magnetic sensor.   3. The metal detection apparatus according to claim 1, wherein the protrusion has a row shape extending in at least one of a conveyance direction of the inspection object or a direction orthogonal to the conveyance direction.   The metal detection device according to claim 1, wherein the protrusion has a conical shape or a circular cylindrical shape with a tip.   The magnetic sensor has a core that provides an elongated magnetic path for a magnetic field to be measured, and a detection coil wound around the core, and the magnetic moment of the core is periodically with respect to the longitudinal direction of the core. 5. The metal detection device according to claim 1, wherein the metal detection device includes an orthogonal fluxgate sensor that supplies an alternating current to the core so as to face in an orthogonal direction. 6.

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