JP5779273B1 - Metal detector sensor and metal detector - Google Patents

Abstract

An object of the present invention is to detect a minute metal foreign object with high accuracy while adapting to various situations. A sensor coil 11 in which a conducting wire 13 is wound around a core 12 to generate a magnetic field for detection, and a magnetization of a metallic foreign object is arranged so as to generate a magnetic field for magnetization in a range covered by the magnetic field of the sensor coil 11. In the metal detection sensor 10A, which includes a magnet 14A as a means and detects a metal foreign object in the inspection object with the sensor coil 11, when the inspection object moves in the magnetic field for magnetization, the packaging portion or the inspection object itself When an eddy current magnetic field is formed in the eddy current magnetic field, which may lead to erroneous detection or a decrease in detection accuracy, the detection magnetic field reduces the eddy current to a level that does not cause extinction or erroneous detection. It is assumed that the sensor coil 11 functions as a canceling magnetic field, and the sensor coil 11 functions as a metallic foreign matter detecting unit and at the same time as an eddy current canceling unit. [Selection] Figure 1

Description

  The present invention relates to a metal detection sensor for detecting a metallic foreign object of a ferromagnetic material mixed in a product and a metal detector provided with the same, in particular, a package having a layer made of a nonmagnetic metal such as an aluminum material or the like. The present invention relates to a metal detection sensor and a metal detector that detect a minute metal foreign matter mixed in a high-concentration electrolyte solution-containing product with high accuracy.

  Conventionally, there are various known methods for detecting ferromagnetic metallic foreign matter mixed in products such as foods and pharmaceuticals. For example, a magnetic field generating coil is energized to form a magnetic field, It is well known to detect the mixed metal foreign object by detecting the influence of the metal foreign object on the magnetic field when passing through the magnetic field receiving coil.

  However, if the object to be inspected is covered with a packaging container or packaging bag having electrical conductivity by aluminum vapor deposition or aluminum foil, an eddy current is generated in the packaging part according to the passing speed in the magnetic field. By forming a magnetic field, there is a problem that it is difficult to detect metallic foreign matter inside the package. In addition, even when the object to be inspected is a product in which an electrolyte solution with a high concentration often found in liquid foods is enclosed, eddy currents are generated by moving in a magnetic field. It becomes difficult to detect.

  To solve this problem, the present inventor disclosed in Japanese Patent Application Laid-Open No. 2004-85439 a sensor coil that generates an alternating magnetic field and a magnet that is arranged in contact with the core of the sensor coil and generates a static magnetic field to magnetize a metal foreign object. By providing a weak magnetic field that does not generate eddy currents in the sensor coil to a package made of a metal having a low relative permeability such as aluminum, the reaction of metallic foreign matter having a higher relative permeability than this We have proposed a metal detection sensor that makes it easy to detect.

  However, when trying to reduce the effects of eddy currents generated in packaging materials using a weak magnetic field as described above, a large amplification factor is required to obtain a practical foreign substance output signal using this method, and external noise There is a drawback that it is easy to be affected. Also, in recent manufacturing sites, there is a tendency to require a large amount of short-time processing such that the conveyance speed exceeds 100 m / min in the foreign substance inspection process, and as the conveyance speed increases, aluminum packaging or high-concentration electrolyte encapsulated products themselves As a result, the eddy current generated at the time increases, and it is more difficult to detect fine metal foreign objects with high accuracy.

  On the other hand, in Japanese Patent Laid-Open No. 2003-66156, the detection means is arranged at a remote position where the magnetic field generated by the magnetizing means does not reach, so that eddy current is not generated in the inspected object itself and erroneous detection is avoided. Technology has been proposed. In this technology, the aluminum packaged product or the electrolyte-filled product itself is a non-magnetic material, so it is not magnetized by the magnetizing means, but an eddy current is generated while passing through the magnetizing magnetic field. It is intended to detect the magnetism remaining on the metal foreign object at a remote position that is not affected.

  However, if the detecting means is arranged at a position away from the influence of the magnetizing means, the magnetized metal foreign object will be demagnetized at the detecting position, so that practical detection accuracy can be improved. It is practically difficult to secure. Further, disposing the magnetizing means and the detecting means at a distance from each other leads to an increase in the size of the metal detector, which requires a large arrangement space and increases the cost. Furthermore, conventional metal detectors including this method still have difficulty in detecting extremely fine metal foreign objects in millimeters with high accuracy, and are not sufficiently capable of meeting the demands of food and pharmaceutical manufacturing sites. Is the current situation.

JP 2004-85439 A JP 2003-66156 A

  The present invention is intended to solve the above-described problems, and an object of the present invention is to make it possible to detect even a fine metal foreign object with high accuracy while dealing with various situations.

Accordingly, the present invention provides a sensor coil in which a conducting wire is wound around a core to generate a magnetic field for detection when energized, and a magnetic field for magnetization in a range covered by the magnetic field generated by the sensor coil. A metal detection sensor for detecting the metal foreign object in the inspection object with the sensor coil, and when the inspection object moves in the magnetic field for magnetization, In the case where an eddy current magnetic field is formed by generating eddy current in the inspection object itself, which may lead to erroneous detection or a decrease in detection accuracy, the detection magnetic field causes the eddy current to disappear or misdetect. The sensor coil acts as a canceling magnetic field that reduces to a level where it does not occur. Are the ones, aspects of the cancel field, the relative eddy current magnetic field due to the eddy current to occur inspection object is assumed based on the detection conditions including the material and transport speed of the object to be inspected, the It is characterized by being a magnetic field with a level strength and the same frequency and antiphase, or an alternating magnetic field with a frequency of 1/2 to 1/20 and a frequency of 2 to 50 times .

When the package or product itself is a highly conductive test object such as an aluminum package or a high-concentration electrolyte solution-enclosed product, an eddy current magnetic field is generated in the test object due to the magnetic field for magnetizing foreign metal, and detection accuracy is improved. In this way, the eddy current generated in the inspection object by the magnetic field for detection is generated while the magnetic field for detection is generated by the sensor coil so as to overlap the magnetic field for magnetization. by was manner to eliminate or reduce, while being compact and simple structure, high ones, the detection accuracy can be realized and Do Ri, and, what is effectively possible to reduce the influence on the detection accuracy due to eddy currents It becomes.

  Further, in the above-described metal detection sensor, the magnet is a permanent magnet, and is arranged in contact with the core of the sensor coil while making the center positions in the inspection object passage direction coincide with each other. And the detecting means and the canceling means are integrated, the magnetic field for magnetization and the magnetic field for detection and cancellation are completely overlapped, and the detection accuracy is further increased. Since it becomes a compact and simple structure, it becomes possible to carry out with a minimum arrangement space in addition to enabling high-precision detection at low cost.

  Alternatively, the magnet is a permanent magnet, and two grooves are formed in parallel on the surface on the detection side in the major axis direction and the cross-sectional shape cut in the minor axis direction is an E-shaped core. A plurality of S-poles and N-poles are arranged on the side surface on the long-diameter side so as to be alternately arranged in the short-diameter direction coinciding with the inspection object passing direction, and the magnetizing means and the canceling means are integrated. Therefore, efficient magnetization and detection can be performed with a minimum magnetic force.

  Furthermore, in the above-described metal detection sensor, the core is formed in a rod shape and is disposed with the major axis direction perpendicular to the inspection object passing direction, and a projection formed by projecting the center part in the minor axis direction of the detection side surface. Is extended or continuously provided along the major axis direction, and the magnetic field lines passing through the protrusions have a higher magnetic flux density than the magnetic field lines passing through other parts. A magnetic field enables highly accurate detection and reliable cancellation of eddy currents.

  In addition, a metal foreign object exists in the inspection object based on one of the above-described metal detection sensors disposed in the conveyance path for conveying the inspection object and a detection signal from the metal detection sensor. If the metal detector is provided with a control means for determining whether or not it is, it is possible to detect a metal foreign object with high accuracy corresponding to various situations.

  In this case, the metal detection sensor is separate from the control means and is operable while being connected to the control means by wireless communication or wired communication. By doing so, it is possible to arrange only the compact metallic foreign matter detection means on the conveyance path of the inspection line and to arrange the control means at another position, so that the arrangement space on the inspection line can be minimized. At the same time, it is possible to make it less difficult to perform maintenance, for example, by adopting a mode in which moisture and corrosion prevention measures are easily taken at the manufacturing site.

  According to the present invention, in which a magnetic field for detection is generated by a sensor coil so as to overlap with a magnetic field for magnetization, an eddy current generated in an object to be inspected is canceled. It can be detected with high accuracy while dealing with various situations.

(A) is a top view of the metal detection sensor which is 1st Embodiment in this invention, (B) is the longitudinal cross-sectional view expanded by the AA of (A). FIG. 2 is a front view of a metal detector provided with the metal detection sensor of FIG. FIG. 3 is a circuit layout diagram of a detection unit including a metal detection sensor of the metal detector of FIG. 2. It is a longitudinal cross-sectional view which shows the state of the magnetic field by the metal detection sensor of FIG. It is a front view which shows the application example of the metal detector of FIG. It is a front view of the other application example of the metal detector of FIG. It is a longitudinal cross-sectional view of the metal detection sensor which is the 2nd Embodiment in this invention. It is a longitudinal cross-sectional view which shows the application example of the metal detection sensor of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1A is a plan view of a metal detection sensor 10A according to the first embodiment of the present invention, and FIG. 1B shows an enlarged cross-sectional view along the line AA. The metal detection sensor 10A includes a sensor coil 11 in which a conductive wire 13 is wound around a core 12 having an E-shaped cross section formed by stacking thin electromagnetic steel plates into a rod shape, and a magnetic field for detection is generated by energization, and the sensor coil 11 is provided so as to generate a magnetic field for magnetization in the range covered by the magnetic field 11 and magnetize the metal foreign object.

  More specifically, a plate-like magnet is formed so that the center positions in the minor axis direction coincide with each other on the surface (hereinafter referred to as “bottom surface”) opposite to the detection side surface (hereinafter referred to as “top surface”) of the core 12. 14A is arranged in close contact, and the magnet 14A is composed of a plurality of permanent magnets as magnet elements (not shown in the figure), and these magnets are continuously arranged with the magnetic poles alternately directed to the bottom surface of the core 12. A static magnetic field for magnetization is formed on the upper surface side through the core 12.

  Further, a case 15 made of a ferromagnetic metal having a U-shaped cross-section with an open top is disposed so as to cover the bottom surface side and both side surfaces of the magnet 14A and the sensor coil 11, and this case provides a magnetic field. It functions as a yoke concentrated on the upper surface side (detection side). Furthermore, on the upper surface of the core 12, a protrusion 12 a is formed in a wall shape along the major axis direction.

  By providing this protrusion 12a, the magnetic field lines passing through the portion have a higher magnetic flux density than the magnetic field lines passing through the other portion on the upper surface side of the core 12, and therefore, it can be intensively detected at the upper position. Higher detection accuracy can be realized. The protrusion 12a may be formed by fixing the central part of the upper surface side of the core 12 as it is, or by fixing a ferromagnetic component separate from the core 12. Further, as shown in FIG. 1A, in addition to the shape in which the wall is extended linearly in plan view, the shape may be zigzag in plan view or a shape in which constituent elements that are short in the longitudinal direction are continuously provided.

  And when such a metal detection sensor 10A moves in the magnetic field for magnetization by the magnet 14A, an eddy current magnetic field is formed by generating an eddy current in the packaging portion or the inspection object itself. A mode in which the magnetic field for detection by the sensor coil 11 acts as a canceling magnetic field that reduces eddy currents generated in the inspection object to a level that does not cause annihilation or erroneous detection, when erroneous detection or reduction in detection accuracy may occur. Thus, the sensor coil 11 functions as a metallic foreign matter detecting means and at the same time as an eddy current canceling means, which is the greatest feature of the present invention.

  FIG. 2 shows a metal detector 1A equipped with the metal detection sensor 10A of FIG. 1, such as a product having a package made of an aluminum vapor-deposited sheet or an aluminum foil sheet, a product filled with a high-concentration electrolyte solution, and the like. For products that tend to be difficult to detect metallic foreign objects due to eddy currents in the packaging or product itself when passing through a magnetic field for magnetization, it is possible to detect even fine metallic foreign objects in millimeters with high accuracy. It is intended.

  The metal detector 1A is disposed on the lower surface side of the belt 30 in the middle of a conveyance path by the conveyance unit 3 and a conveyance unit 3 including a belt conveyor having a belt 30 that operates in an endless track by driving a motor 4. The detection unit 5A (not shown) provided with the metal detection sensor 10A and the control unit 2A provided with the control means 20 for executing various controls including determination of contamination of metal foreign matter are conveyed from the upstream side of the conveyance path. After the detected object 50 is detected by the optical sensor 7, the control unit 2A determines whether or not there is a metal foreign object based on a signal detected when passing over the metal detection sensor 10A.

  FIG. 3 is a circuit layout diagram for explaining the configuration and principle of the detection unit 5A having the metal detection sensor 10A described above. The detection unit 5A magnetizes a metal foreign object with a static magnetic field M1 generated by a magnet 14A made of a permanent magnet, and changes the magnetic poles to affect the alternating magnetic field M2 by the sensor coil 11, which is a bridge circuit that is a detection circuit. This is a method of detecting at 51. Therefore, the magnet 14A is arranged in a range where the static magnetic field M1 is covered by the alternating magnetic field M2 generated by applying an alternating current having a predetermined frequency and a predetermined intensity to the sensor coil 11 from the alternating frequency power supply 100. In this embodiment, the two magnetic fields overlap each other.

  The signal detected by the bridge circuit 51 is amplified by the differential amplifier 21 on the control unit 2A side and then input to the control means 20 having a digital computer to determine the presence or absence of metal foreign matter. By taking the current from the alternating frequency power supply 100 and summing it with the phase-inverted signal, the signal portion of the AC power supply is erased, and only a predetermined metal foreign object signal is taken into the digital computer for determination. Is common to the metal detector according to Patent Document 1 described above.

  As described above, in the present invention, the alternating magnetic field M2, which is a magnetic field for detection by the sensor coil 11, acts as a canceling magnetic field that reduces eddy currents generated in the inspection object to a level that does not cause annihilation or erroneous detection. It is characterized by the aspect. Specifically, when detecting a metal foreign object with a metal detector or the like of the method according to Patent Document 1, the magnetic field for detection by the sensor coil is set to the same level as that of the eddy current magnetic field generated in the inspection object. In addition, a magnetic field having the same frequency, or a harmonic alternating magnetic field having a strength of 1/2 to 1/20 and a frequency of 2 to 50 times (an alternating magnetic field having a frequency higher than the frequency of the eddy current magnetic field generated in the inspection object). ).

  The inventor of the present application has found through experiments that an eddy current (magnetic field) generated in the object to be inspected can be suppressed or extinguished by flowing an alternating current that forms a canceling magnetic field in such a manner to the sensor coil. It depends. Further, in the present embodiment, it is an effective mode compared to a method in which a canceling magnetic field having the same level and the same frequency is formed by a sensor coil with respect to a magnetic field caused by eddy currents generated at various positions in the inspection object. Since the method of forming a canceling magnetic field using a harmonic alternating magnetic field having a certain width is easier, the case of using this method will be described.

  In this method, the frequency, amplitude value, and phase of the alternating current that flows through the sensor coil are different from each other because the frequency and amplitude values of eddy currents that are generated depend on various conditions such as the material of the inspection object and the conveyance speed. It should be set as appropriate within the range of the above-described mode according to the current state. Ideally, complete annihilation of the eddy current is desirable, but the eddy current generated in the inspection object has a harmonic component with a smaller amplitude than this. The effect of significantly reducing false signals caused by eddy currents is recognized.

  Note that the harmonic alternating magnetic field used as the canceling magnetic field described above is 1/3 to 1/5 of the assumed eddy current magnetic field from the viewpoint of being able to detect a fine metallic foreign object in millimeters with high accuracy. The strength is preferably 3 to 10 times the frequency. The strength of the magnetic field is the same as the magnitude of the waveform when the magnetic field is detected by the wound coil.

  FIG. 4 shows the state of the magnetic field by the metal detection sensor 10A described above. The static magnetic field generated by the magnet 14A is indicated by M1, and the alternating magnetic field generated by the sensor coil 11 is indicated by M2. These magnetic fields overlap each other, and both of them have a dense magnetic flux above the core 12. This is because the magnetic field lines are concentrated on this portion by providing the protrusion 12a higher than the other portion at the center of the upper surface of the core 12. Further, the presence of the case 15 makes it difficult for the magnetic field lines to spread laterally.

  Next, the present invention will be described in more detail with reference to an embodiment using an actual metal detector. The metal detector used has the same configuration as the metal detector 1A shown in FIG. 2, the detection unit has the same configuration as the detection unit 5A shown in FIG. 3, and the metal detector is the metal detector 10A shown in FIG. A neodymium magnet is used as the magnetizing magnet. In addition, the conveyance speed by the belt is set to 40 m / min, and when a foreign object is detected by the control unit, a buzzer is sounded to notify.

A plastic confectionery packaging bag made of aluminum deposited on the inner surface of a 12.5 cm x 17.0 cm envelope is used as the aluminum package for the object to be inspected, and an iron wire with a diameter of 0.5 mm x 3.0 mm as a metallic foreign object. (1) was used. Based on the result of the simulation, the magnitude of the alternating voltage applied to the sensor coil is assumed to be 1 V, assuming that a canceling magnetic field of 10 times the frequency of the eddy current magnetic field generated from the aluminum packaging bag is formed by 1/3. and _P-P, the frequency and 400Hz.

  Then, A: wire alone, B: aluminum packaging bag without wire, C: aluminum packaging bag with wire inserted, and 10 foreign object inspections, respectively, A indicates all foreign object detection, B All did not report foreign object detection, and C all reported foreign object detection. By the way, the same method was applied to the method in which the alternating voltage applied to the sensor coil is cut off and no cancel magnetic field is formed in this method, but A is all informing foreign object detection, B is all informing foreign object detection, and C is All foreign matter detection was reported. As a result, it was found that the metal detection sensor 1A according to the present embodiment can detect fine metal foreign matter in the aluminum packaging bag with high accuracy.

  FIG. 5 shows a metal detector 1B as an application example of the above-described metal detector 1A. In this example, it is assumed that the object to be inspected has a certain thickness. The magnet 18 is supported at a predetermined height above the metal detection sensor 10A, and the detectable range is expanded upward. The other parts are the same as those described above.

  However, when the magnet 18 is supported above the conveyor belt in this way, the magnet 18 is excessively swung due to vibration generated in the conveying operation or vibration applied from the outside, and the possibility of erroneous detection increases. Therefore, in this example, when the three-dimensional vibration detector 16 is disposed above the arch-shaped member and the detection signal is input to the control unit 2B, there is a level of vibration that affects detection. The control means 20 cancels the influence of the vibration.

  FIG. 6 shows a metal detector 1C as another application example of the metal detector 1A of FIG. In this example, the metal detector 1C is configured only by the detection unit 5C and the control unit 2C, and does not include the transport unit, and is used in combination with the existing belt conveyor device 8. . Further, in this example, the detection unit 5C attached to the belt conveyor device 8 is separate from the control unit 2C, and is used in a state in which both are connected by wireless communication.

  That is, the wireless communication means 55 is provided in the detection unit 5C including the metal detection sensor 10A, and the wireless communication means 25 is provided in the control unit 2C including the control means 20, and the metal detection sensor 10A. The detected detection data is continuously transmitted to the control unit 2C. For this reason, for example, when foreign matter inspection is performed in a food factory that manufactures pickles, etc., when the control unit including a digital computer is integrated with the detection unit, it is likely to cause corrosion of the device due to indoor moisture and salt As in this example, the control unit 2C is separated from the detection unit 5C and is connected remotely, so that the control unit 2C is arranged in a separate room to corrode the parts including precision parts. The situation can be easily avoided. In addition, since the detection unit 5C is configured separately and made compact, the inside of the detection unit 5C can be easily brought close to a gas / liquid-tight state. It becomes easy to take measures against dust and wetness.

  FIG. 7 shows a cross-sectional view of a metal detection sensor 10B according to the second embodiment of the present invention. In this embodiment, the magnet 14B is arranged on at least one major axis side surface of the core 12 having an E-shaped cross section, and the S pole and the N pole alternate in the inspection object passage direction (minor axis direction). A feature is that the magnetizing means and the canceling means are integrated by adopting a configuration in which a plurality of permanent magnets are continuously arranged so as to be lined up with each other.

  The inventor of the present application experimented that, by adopting such a permanent magnet arrangement method, the magnetic field is concentrated on the detection side (upper side) and efficient magnetization and detection can be performed with a minimum magnetic force. Because it was found by. Moreover, it is preferable that the magnet 14B attached to the core 12 has a length in the major axis direction similar to that of the core 12, similarly to the magnet 14A in the above-described embodiment. And this metal detection sensor 10B is applicable to all the metal detectors mentioned above.

  As shown in FIG. 8, the magnet for magnetizing attached to the core 12 is a magnet 14C in which a plurality of permanent magnets are arranged in a Halbach array, so that the magnetic field can be detected. (Upward) can be concentrated to some extent, and the range that can be detected with high accuracy from the sensor position can be expanded.

  As described above, regarding the metal detection sensor and the metal detector for detecting the metallic foreign matter mixed in the product, even if the mixed metallic foreign matter is fine, the present invention can cope with various situations. It became possible to detect with accuracy.

  1A, 1B, 1C metal detector, 2A, 2B, 2C control unit, 3 transport unit, 5A, 5C detection unit, 10A, 10B, 10C metal detection sensor, 11 sensor coil, 12 core, 12a protrusion, 13 conductor, 14A , 14B, 14C, 18 Magnet, 25, 55 Wireless communication means, 50 Inspected object

Claims (6)

A sensor coil in which a conducting wire is wound around a core and generates a magnetic field for detection when energized, and a magnet that is arranged so as to generate a magnetic field for magnetization in a range covered by the sensor coil and functions as a magnetizing means for metal foreign matter In the metal detection sensor for detecting the metal foreign matter in the inspection object with the sensor coil,
When the object to be inspected moves in the magnetic field for magnetization, an eddy current magnetic field is formed by generating an eddy current in the packaging part or the object to be inspected itself, which may cause erroneous detection or decrease in detection accuracy. In some cases, the detection magnetic field acts as a canceling magnetic field that reduces eddy current generated in the inspection object to a level that does not cause annihilation or erroneous detection, and the sensor coil is a metallic foreign object detection means. At the same time, it is assumed to function as a means for canceling the eddy current, and the mode of the canceling magnetic field is assumed to occur in the inspection object according to inspection conditions including the material and transport speed of the inspection object. that due to eddy current to the eddy current magnetic field, an alternating magnetic field by 2-50 times the frequency intensity of the magnetic field of the same intensity level and opposite phase at the same frequency or 1 / 2-1 / 20, Metal detection sensor, wherein the door.   The magnet is a permanent magnet, and is arranged in contact with the core of the sensor coil in a state in which the center positions in the inspection object passing direction coincide with each other, and the magnetizing means, the detecting means, and the canceling means are integrated. The metal detection sensor according to claim 1, wherein the metal detection sensor is formed.   The magnet is a permanent magnet, and has at least one major axis side of a core in which two grooves are formed in parallel on the surface on the detection side and formed in the major axis direction and the cross-sectional shape cut in the minor axis direction is an E-shape. A plurality of S poles and N poles are continuously arranged in the minor axis direction coinciding with the inspection object passing direction, and the magnetizing means, the detecting means and the canceling means are integrated. The metal detection sensor according to claim 1, wherein   The core is formed in a rod shape and is arranged with the major axis direction perpendicular to the inspection object passage direction, and a projection formed by projecting the center part in the minor axis direction of the detection side surface extends along the major axis direction or 4. The metal detection sensor according to claim 1, wherein the metal detection sensor is provided in a row and has a magnetic flux density higher than a magnetic force line passing through the protruding portion than a magnetic force line passing through the other portion.   5. The metal detection sensor according to claim 1, 2, 3, or 4 disposed in the middle of a conveyance path for conveying the inspection object, and a metal in the inspection object based on a detection signal from the metal detection sensor. A metal detector comprising: control means for determining whether or not a foreign object exists.   6. The metal detection sensor according to claim 5, wherein the metal detection sensor is separate from the control unit and is operable while being connected to the control unit by wireless communication or wired communication. Metal detector.

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