JP2014092365A - Metal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detector capable of stably detecting fine metallic foreign matter in a body to be inspected with high sensitivity by reducing an influence of disturbance noise by emphasizing a foreign matter signal, and also specifying a width-directional position of the foreign matter.SOLUTION: A metal detector 10 includes: a magnetization part 30 which magnetizes metallic foreign matter (m) in a body W to be inspected in a predetermined magnetization direction; a detection head 40 which has a plurality of magnetic sensor pairs of upper magnetic sensors 41a-41e and lower magnetic sensors 42a-42e having sharp directivity in the magnetization direction of the magnetization part 30 in an orthogonal direction orthogonal to a conveyance direction of the body W to be inspected, and detects a residual magnetic component of the metallic foreign matter (m); difference calculation means 80 of calculating differences between detection signals from the upper magnetic sensors 41a-41e and lower magnetic sensors 42a-42e by the magnetic sensor pair; and determination means 53 of determining whether there is metal in the body W to be inspected and its position in the orthogonal direction upon the basis of an output signal from the difference calculation means 80.

Description

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

  Conventionally, as this type of metal detection device, a metal detection device that detects the presence or absence of metal foreign matter in an inspection object such as food based on a change in magnetic field caused by the passage of the inspection object. In addition to providing a sensor, one or more detection sensors are provided via a conveyance path for one or more of the plurality of magnetic sensors, so that composite detection is performed when the inspection object is not being conveyed. A technique is known in which a disturbance noise level included in a detection signal is reduced by setting a connection state between magnetic sensors so that the signal level of the signal is minimized (see, for example, Patent Document 1). ).

Specifically, the one described in Patent Document 1 is configured such that the magnetic sensors connected in this manner are connected by differentially connecting the magnetic sensors facing each other in the vertical direction and adding and connecting a pair of magnetic sensors in the transport direction that are differentially connected. The detection signals from the sensors are combined to reduce the disturbance noise level included in the detection signals.
JP 2005-227029 A

  However, in the conventional metal detection device described in Patent Document 1, only the difference is taken from the magnetic sensor facing up and down, and the relationship between the direction of magnetization and the directivity of the magnetic sensor has not been studied. The detection signal due to the metal foreign object could not be emphasized.

  In addition, since the detection signal of the magnetic sensor is a scalar, the difference calculation based on whether the phase (positive / negative) of the detection signal value from the upper and lower magnetic sensors is in-phase or reverse is not performed.

  Therefore, minute metallic foreign matter in the inspection object cannot be detected with high sensitivity due to the influence of disturbance noise from a motor or the like that drives the conveyor belt.

  In addition, in the conventional metal detection device described in Patent Document 1, since a plurality of magnetic sensors are not arranged in the orthogonal direction (width direction of the conveyance path) orthogonal to the conveyance direction, the position of the metal foreign object in the orthogonal direction Could not be identified. Further, since the detection sensitivity is low at the intermediate position between the upper and lower magnetic sensors, there are cases in which it is not possible to detect the metallic foreign matter present at this intermediate position.

  Therefore, the present invention has been made to solve the above-described conventional problems, and by emphasizing the foreign matter signal, the influence of disturbance noise is reduced and the minute metallic foreign matter in the inspection object is stabilized. It is an object of the present invention to provide a metal detection device that can detect with high sensitivity and can specify the position in the width direction of a foreign substance.

  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 a metal in the test object transported by the transport unit in a predetermined magnetization direction, There are a plurality of magnetic sensor pairs in the orthogonal direction perpendicular to the conveyance direction of the object to be inspected, which are an upper magnetic sensor and a lower magnetic sensor that are opposed to each other across the conveyance path and have sharp directivity in the magnetization direction of the magnetizing means. A detection head for detecting the residual magnetic component of the metal in the inspection object magnetized by the magnetizing means with the upper magnetic sensor and the lower magnetic sensor, and the upper magnetic sensor for each magnetic sensor pair. And a difference calculating means for calculating a difference between detection signals from the lower magnetic sensor, and a judgment for determining the presence / absence of metal in the inspection object and the position in the orthogonal direction based on an output signal from the difference calculating means. Characterized by comprising a means.

  With this configuration, since the foreign object signal is emphasized by calculating the difference between the detection signals from the upper magnetic sensor and the lower magnetic sensor by the difference calculation means, the foreign object signal can be stably increased without causing erroneous determination of the foreign object due to disturbance noise. Foreign matter can be detected with sensitivity.

  In addition, since there are a plurality of magnetic sensor pairs composed of the upper magnetic sensor and the lower magnetic sensor in the orthogonal direction orthogonal to the conveyance direction of the object to be inspected, the determination means has a metal in the object inspected for each magnetic sensor pair. The position of the metal foreign object in the orthogonal direction can be specified.

  Also, by calculating the difference between the detection signals from the upper magnetic sensor and the lower magnetic sensor and emphasizing the foreign matter signal, the metallic foreign matter present at the intermediate position between the upper magnetic sensor and the lower magnetic sensor is also enhanced by the enhancement of the foreign matter signal. It can be detected with high sensitivity.

  Therefore, by emphasizing the foreign matter signal, the influence of disturbance noise can be reduced, and the minute metal in the inspection object can be stably detected with high sensitivity, and the position of the metallic foreign matter in the orthogonal direction can be specified. Can do.

  In addition, the metal detection device according to the present invention includes shielding means that surrounds the detection head from the outside and has an opening through which the transport path passes, and shields disturbance noise that enters the detection head. It is characterized by that.

  With this configuration, the disturbance noise from the outside of the detection head is shielded by the shielding means, and the disturbance noise entering from the opening of the shielding means has the same phase in the detection signals of the upper magnetic sensor and the lower magnetic sensor, so that the difference calculation means Can be canceled by taking the difference.

  In the metal detector according to the present invention, the transport means includes a transport surface on which an object to be inspected is placed and a motor that moves the transport surface, and the transport surface and the motor are the upper magnetic sensor. And the lower magnetic sensor.

  With this configuration, the distance from the motor to the upper magnetic sensor is equal to the distance from the motor to the lower magnetic sensor. Therefore, the disturbance noise amplitude from the motor detected by the upper magnetic sensor and the motor detected by the lower magnetic sensor The disturbance noise component included in the detection signal from the upper magnetic sensor and the disturbance noise component included in the detection signal from the lower magnetic sensor can be canceled by the difference calculation means.

  The present invention enhances the foreign object signal to reduce the influence of disturbance noise and stably detect a minute metal foreign object in the inspection object with high sensitivity and specify the position of the metal foreign object in the width direction. It is possible to provide a metal detection device that can be used.

It is a perspective view of the metal detection apparatus which concerns on embodiment of this invention. It is a top view of the metal detection apparatus which concerns on embodiment of this invention. It is CC 'sectional drawing of FIG. It is DD 'sectional drawing of FIG. It is a circuit block diagram which shows an example of the magnetic sensor of the metal detection apparatus 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 a figure which shows the output signal from the difference calculation means of the metal detection apparatus which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the configuration will be described.

  As shown in FIGS. 1 to 4, the metal detection device 10 is configured to convey a conveyor 20 that conveys the inspection object W in the conveyance path 20 a and a metal foreign object m in the inspection object W that is conveyed by the conveyor 20 to a predetermined level. A magnetic sensor comprising a magnetized portion 30 that is magnetized in the magnetization direction, and upper magnetic sensors 41a to 41e and lower magnetic sensors 42a to 42e that are opposed to each other across the conveyance path 20a and have sharp directivity in the magnetization direction of the magnetized portion 30. A plurality of pairs are provided in an orthogonal direction (indicated by an arrow B) orthogonal to the conveyance direction of the inspection object W, and the residual magnetic component of the metal foreign matter m in the inspection object W magnetized by the magnetized portion 30 is set on the upper side. The detection head 40 detected by the magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e, and the difference between the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e for each magnetic sensor pair. A difference calculation unit 80 for output, and a determination unit 53 the position of the presence and the orthogonal direction of the metal foreign object m in the object to be inspected is W, the based on the output signal from the difference calculation unit 80.

  In addition, the metal detection device 10 includes a magnetic shield 49 that surrounds the detection head 40 from the outside and has an opening through which the transport path 20 a passes, and shields disturbance noise that enters the detection head 40.

  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.

  The conveyor 20 includes a motor 90 for rotating the belt 21 as a conveyance surface at one end in the axial direction of the conveyance roller 22b. The motor 90 can be a noise source of disturbance noise that enters the magnetic detection region 45 inside the detection head 40. The upper surface of the belt 21, the transport rollers 22a and 22b, and the motor 90 are disposed at a substantially middle position between the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e in the vertical direction. For this reason, the distance from the motor 90 to the upper magnetic sensors 41a to 41e is equal to the distance from the motor 90 to the lower magnetic sensors 42a to 42e.

  A known magnetized portion 30 including an upper magnetic pole 30a and a lower magnetic pole 30b that are vertically opposed to each other across the conveyance path 20a is installed at a predetermined position upstream of the detection head 40 in the conveyance path 20a. The magnetized portion 30 applies a magnetic field in the vertical direction between the upper magnetic pole 30a and the lower magnetic pole 30b.

  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, and the metal foreign matter m in the inspection object W is magnetized at a predetermined residual magnetization level.

  For this reason, the magnetization direction of the metal foreign matter m is parallel to the line connecting the upper magnetic pole 30a and the lower magnetic pole 30b (the vertical direction indicated by the arrow H). Further, the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are lines connecting the upper magnetic pole 30a and the lower magnetic pole 30b in order to detect the magnetic flux of the metal foreign matter m magnetized by the magnetized portion 30 satisfactorily. Each has a sharp directivity in a direction (vertical direction indicated by an arrow H) parallel to each other. Note that the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are also spaced apart from each other in the vertical direction indicated by the arrow H with the conveyance path 20a interposed therebetween.

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

  That is, the detection head 40 composed of the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e is disposed at an inclination, and when viewed from above, in a direction orthogonal to the conveying direction of the conveyor 20 (width direction of the conveyor 20). You may make it provide an angle with respect to it.

  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 upper 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. In addition, a plurality of lower magnetic sensors 42 a to 42 e are arranged in the lower head 42 in the orthogonal direction orthogonal to the conveyance direction of the inspection object W, respectively.

  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. In the magnetic detection region 45, the inspection object W passes through the upper head 41 and the lower head 42 at the same time, so the upper magnetic sensors 41a to 41e of the upper head 41 and the lower magnetic sensors 42a to 42e of the lower head 42. Detects magnetism at the same timing for the same part of the inspection object W.

  As shown in FIGS. 1 and 2, a magnetic shield 49 that shields disturbance noise that enters the magnetic detection region 45 inside the detection head 40 is provided around the outside of the detection head 40. 1 and 2, the magnetic shield 49 includes both end portions in the direction indicated by the arrow B (the width direction of the belt 21) that is orthogonal to the conveyance direction of the inspection object W, and the vertical direction (FIGS. 1 and 4). And is provided to surround the transport path 20a so as to wind the detection head 40 from the outside. The magnetic shield 49 has openings that open to the upstream side and the downstream side in the transport direction at the part through which the transport path 20a passes.

  As shown in FIG. 4, the upper magnetic sensors 41 a to 41 e and the lower magnetic sensors 42 a to 42 e have sharp directivities in the same direction as the magnetization direction of the workpiece W by the magnetized portion 30, that is, in the vertical direction indicated by the arrow H. have.

  Therefore, the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e detect only the component in the sharp directivity direction indicated by the vertical arrow H in the magnetic flux of the metal foreign matter m in the inspection object W. can do. Further, the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are only components in the direction of sharp directivity with respect to disturbance noise from the motor 90 entering from the opening on the downstream side in the transport direction of the magnetic shield 49. Is detected. The upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are composed of magnetic sensors having sharp directivity, for example, a magnetic impedance sensor, a Hall element, a magnetoresistive element, and a fluxgate sensor.

  Further, the metal detection apparatus 10 includes a control unit 50 having an AD conversion unit 52, a difference calculation unit 80, a determination unit 53, and a result display unit 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 foreign matter m is mixed in the inspection object W.

  The detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are sent to the AD conversion means 52 provided individually for each of the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e. The detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are converted into AD conversion means 52 while the inspection object W passes through the magnetic detection region 45. Are converted from analog signals to digital signals.

  The detection signal converted into the digital signal by the AD conversion means 52 is calculated by the difference calculation means 80 provided individually for each pair of the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e. It has become.

  That is, in the difference calculation means 80, the difference between the upper magnetic sensor 41a and the lower magnetic sensor 42a, the difference between the upper magnetic sensor 41b and the lower magnetic sensor 42b, and the difference between the upper magnetic sensor 41c and the lower magnetic sensor 42c. The difference between the upper magnetic sensor 41d and the lower magnetic sensor 42d and the difference between the upper magnetic sensor 41e and the lower magnetic sensor 42e are respectively calculated.

  Each output signal from the difference calculation means 80 is input to the determination means 53 connected to the subsequent stage of each difference calculation means 80, and the presence / absence of metal is determined by referring to the determination threshold set in advance by each determination means 53. It is to be judged.

  As described above, the determination unit 53 determines the amount of the metallic foreign object m in the inspection object W based on the difference between the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e calculated by the difference calculation unit 80. Judgment is made. The determination result by the determination unit 53 is displayed by the result display unit 54.

  The determination unit 53 merely determines the presence or absence of the metal foreign object m in the inspection object W based on the difference between the detection signals from the plurality of upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e of the detection head 40. Rather, based on which output signal from the difference calculation means 80 has exceeded the threshold for determination, the position of the metal foreign object m in the inspection object W in the orthogonal direction indicated by the arrow B is calculated, and the result display means 54 To output.

  Further, the determination means 53 is based on the intensity of the detection signals of the upper magnetic sensors 41a to 41e of the upper head 41 and the detection signals of the lower magnetic sensors 42a to 42e of the lower head 42, and the metal foreign matter in the inspection object W. The position in the vertical direction indicated by the arrow H of m is calculated and output to the result display means 54.

  Hereinafter, specific configurations of the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e will be described using orthogonal flux gate sensors which are one of flux gate sensors having sharp directivity. Note that the fluxgate sensor is a known sensor described in, for example, Japanese Patent Application Laid-Open No. 2012-154673, and thus the description thereof is omitted. Since the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e have the same configuration, the lower magnetic sensor 42a will be described below.

  As shown in FIG. 5, in the lower magnetic sensor 42a having sharp directivity, a coil for canceling the input magnetic field is provided as the detection coil 63, and the residual magnetic field is detected by the high sensitivity sensor. A negative feedback configuration is adopted in which a zero position method is employed in which the magnitude of the input magnetic field is detected from the magnitude of the current used to cancel the input magnetic field so as to be zero. The negative feedback configuration employing the zero position method has the advantages of good linearity and a wide dynamic range.

  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. 6 (a) or FIG. 6 (b), the lower magnetic sensor 42a has an U-shaped core 62 made of amorphous wire, so that the input magnetic field can be applied to the left and right legs of the core 62. The magnetic flux change generated regardless of the offset is canceled out, and the occurrence of an offset can be prevented.

  The length of the core 62 of the lower 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.

  In the present embodiment, the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are arranged in the same direction in the sharp directivity direction (the vertical direction indicated by the arrow H), and the detection signals are detected above and below these magnetic sensors. Since the positive / negative (polarity) is reversed, the difference between the detection signals from the upper magnetic sensors 41a to 41e and the detection signals from the lower magnetic sensors 42a to 42e is calculated, thereby enhancing the signal due to the metal foreign matter. .

  Here, when the upper and lower magnetic sensors are arranged in the same direction in the sharp directivity direction, the magnetic flux directed upward from the magnetic detection region 45 with respect to the upper magnetic sensors 41a to 41e is used as a detection signal having a positive (or negative) value. The upper magnetic sensors 41a to 41e and the lower magnetic sensor 42a to 41e are detected so as to detect a magnetic flux directed downward from the magnetic detection region 45 with respect to the lower magnetic sensors 42a to 42e as a detection signal having a negative (or positive) value. The magnetic sensors 42a to 42e are arranged.

  In addition, when the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are arranged in the opposite directions in the sharp directivity direction, the positive and negative (polarity) of the detection signal is the same above and below these magnetic sensors. When the detection signal from one of the magnetic sensors 41a to 41e or the lower magnetic sensors 42a to 42e is converted into a digital signal by the AD conversion means 52, the sign of the detection signal is calculated after the polarity is inverted, or By adding the detection signals from the upper magnetic sensors 41a to 41e and the detection signals from the lower magnetic sensors 42a to 42e with the same sign, the signal due to the metal foreign matter is emphasized.

  Next, the operation will be described.

  Regarding the operation of the metal detection device 10 described with reference to FIGS. 1 to 4, when the inspection object W including the metal foreign matter m passes through the magnetic detection region 45, the upper magnetic sensors 41 a to 41 e and the lower magnetic sensor 42 a. The detection signals from .about.42e are converted from analog signals to digital signals in the AD conversion means 52, respectively.

  Each detection signal converted into a digital signal is input to difference calculation means 80 provided individually for each pair of the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e, and the difference is calculated. The output signal from each difference calculation means 80 is input to the determination means 53 connected to the subsequent stage of the difference calculation means 80.

  As shown in FIG. 7, when the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e converted into digital signals are detection signals 41as to 41es and 42as to 42es, respectively, metal foreign matter m Since the positive and negative (polarity) of the signal by the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are opposite (in opposite phases), the difference is calculated by the difference calculating means 80, so that FIG. As shown, the signal from the metal foreign object m is emphasized.

  In FIG. 7, the signal due to the metal foreign matter m included in the detection signals from the upper magnetic sensors 41 a to 41 e is a positive value, and the signal due to the metal foreign matter m included in the detection signals from the lower magnetic sensors 42 a to 42 e. Is a negative value.

  In FIG. 8, an output signal 80as represents a difference calculated from the detection signal 41as and the detection signal 42as. Similarly, the output signals 80bs, 80cs, 80ds, and 80es are calculated from the difference calculated from the detection signal 41bs and the detection signal 42bs, the difference calculated from the detection signal 41cs and the detection signal 42cs, and the detection signal 41ds and the detection signal 42ds. And the difference calculated from the detection signal 41es and the detection signal 42es.

  Further, since the positive and negative (polarity) of the signal of the disturbance noise is the same (in phase) in the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e, the difference is calculated by the difference calculating means 80, so that FIG. It will be countered as shown.

  The determination unit 53 compares each of the output signals 80as to 80es from each difference calculation unit 80 with a determination threshold value, and if there is an output signal exceeding the determination threshold value, the metal foreign matter m is mixed. The result of the determination to the effect is output to the result display means 54.

  Further, the determination means 53 determines that the metal foreign matter m is mixed in the location of the magnetic sensor corresponding to the output signal exceeding the determination threshold, and the arrow B of the metal foreign matter m in the inspection object W is used. The position in the orthogonal direction shown is calculated and output to the result display means 54.

  Further, the determination means 53 determines that the metal foreign matter m is mixed in the magnetic sensor arrangement location corresponding to the output signal exceeding the determination threshold, and the detection signals of the upper magnetic sensors 41a to 41e of the upper head 41 are detected. Based on the signal strengths of 41as to 41es and the detection signals 42as to 42es of the lower magnetic sensors 42a to 42e of the lower head 42, the position of the metal foreign object m in the inspection object W in the vertical direction is indicated by the arrow H. Calculate and output to the result display means 54. Upon receiving the determination result, the result display means 54 displays the presence / absence and position of the metal foreign matter m in the inspection object W.

  As described above, the metal detection device 10 according to the present exemplary embodiment predetermines the conveyor 20 that conveys the inspection object W in the conveyance path 20a and the metal foreign matter m in the inspection object W that is conveyed by the conveyor 20. A magnetized portion 30 that is magnetized in the magnetization direction, and upper magnetic sensors 41a to 41e and lower magnetic sensors 42a to 42e that face each other across the transport path 20a and have sharp directivity in the magnetization direction of the magnetized portion 30. A plurality of sensor pairs are provided in an orthogonal direction orthogonal to the conveyance direction of the inspection object W, and the residual magnetic components of the metal foreign matter m in the inspection object W magnetized by the magnetizing unit 30 are used as the upper magnetic sensors 41a to 41e. And the difference between detection signals from the detection head 40 detected by the lower magnetic sensors 42a to 42e and the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e for each magnetic sensor pair. And minute calculation unit 80, the determining means 53 the position of the presence and the orthogonal direction of the metal in the object W based on an output signal from the difference calculation unit 80, and further comprising a.

  With this configuration, the difference calculation means 80 calculates the difference between the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e, thereby enhancing the foreign object signal. It is possible to detect a foreign object stably and with high sensitivity without having to.

  Further, since a plurality of magnetic sensor pairs including the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e are provided in the orthogonal direction orthogonal to the conveyance direction of the inspection object W, the determination unit 53 is a magnetic sensor pair. The presence / absence of the metal foreign matter m in the inspection object W can be determined every time, and the position of the metal foreign matter m in the orthogonal direction can be specified.

  Further, by calculating the difference between the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e and emphasizing the foreign substance signal, the intermediate between the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e. The metallic foreign matter m present at the position can also be detected with high sensitivity by enhancing the foreign matter signal.

  Therefore, the influence of disturbance noise can be reduced by emphasizing the foreign matter signal, so that a minute metal in the inspection object W can be stably detected with high sensitivity, and the position of the metallic foreign matter m in the orthogonal direction can be specified. can do.

  In addition, the metal detection device 10 according to the present embodiment includes a magnetic shield that surrounds the detection head 40 from the outside and has an opening through which the conveyance path 20a passes to shield disturbance noise that enters the detection head 40. 49 is provided.

  With this configuration, disturbance noise from the outside of the detection head 40 is shielded by the magnetic shield 49, and disturbance noise that has entered from the opening of the magnetic shield 49 is detected by the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e. Therefore, the difference calculation means 80 can cancel the difference.

  Moreover, the metal detection apparatus 10 according to the present embodiment includes a conveyor 20 having an upper surface of a belt 21 as a mounting surface on which the inspection object W is mounted, and a motor 90 that moves the belt 21. The upper surface of the motor 21 and the motor 90 are arranged at a substantially middle position between the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e.

  With this configuration, since the distance from the motor 90 to the upper magnetic sensors 41a to 41e is equal to the distance from the motor 90 to the lower magnetic sensors 42a to 42e, disturbance noise from the motor 90 detected by the upper magnetic sensors 41a to 41e. And the amplitude of the disturbance noise from the motor detected by the lower magnetic sensors 42a to 42e become equal, and the disturbance noise component included in the detection signals from the upper magnetic sensors 41a to 41e and the lower magnetic sensors 42a to 42e. The disturbance noise component included in the detected signal can be canceled by the difference calculating means 80 to zero.

  As described above, the metal detection device according to the present invention can reduce the influence of disturbance noise by enhancing the foreign object signal, and can stably detect a minute metal foreign object in the inspection object with high sensitivity. It is useful as a metal detection device that detects the presence or absence of a metal foreign object in an inspection object such as food.

10 Metal detection device 20 Conveyor (conveyance means)
20a Conveying path 21 Belt (conveying surface)
30 Magnetized part (magnetizing means)
30a Upper magnetic pole 30b Lower magnetic pole 40 Detection head 41 Upper head 41a-41e Upper magnetic sensor 42a-42e Lower 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 80 Difference calculation means 90 Motor m Metal foreign material W Inspected object

Claims (3)

A transport means for transporting the inspection object in the transport path;
Magnetizing means for magnetizing a metal in the inspection object conveyed by the conveying means in a predetermined magnetization direction;
A plurality of magnetic sensor pairs, each of which is an upper magnetic sensor and a lower magnetic sensor, facing each other across the conveyance path and having a sharp directivity in the magnetization direction of the magnetizing means, are perpendicular to the conveyance direction of the inspection object. A detection head that detects a residual magnetic component of a metal in the inspection object magnetized by the magnetizing means, using the upper magnetic sensor and the lower magnetic sensor;
Difference calculating means for calculating a difference between detection signals from the upper magnetic sensor and the lower magnetic sensor for each magnetic sensor pair;
A metal detection apparatus comprising: determination means for determining presence / absence of a metal in the inspection object and a position in the orthogonal direction based on an output signal from the difference calculation means.   2. The apparatus according to claim 1, further comprising a shielding unit that surrounds the detection head from outside and has an opening through which the conveyance path passes, and shields disturbance noise that enters the detection head. Metal detector. The transport means has a transport surface on which an object to be inspected is placed, and a motor that moves the transport surface,
The metal detection device according to claim 1, wherein the transport surface and the motor are disposed at a substantially intermediate position between the upper magnetic sensor and the lower magnetic sensor.

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