JP6590525B2 - Metal detector - Google Patents

Description

  The present invention relates to a metal detector that detects the presence or absence of metal in an object to be inspected, such as food or clothing.

  Conventionally, a metal detector described in Patent Document 1 is known as this type of metal detector. The conventional one described in Patent Document 1 has a conveyor that conveys an object to be inspected in a conveyance path, a magnetized portion that magnetizes metal in the object to be inspected conveyed by the conveyor, and a sharp directivity in the width direction of the conveyor And a plurality of magnetic sensors arranged in the width direction, and a detection head for detecting a residual magnetic component of a metal in an object to be inspected magnetized by a magnetized portion, and wound around a core of each magnetic sensor A plurality of AD conversion means for converting analog signals from the windings into digital signals, and a plurality of determination means connected to each AD conversion means for determining the presence or absence of metal in the inspected object based on the output signal; It has.

  With this configuration, the conventional one can detect a minute metal in the inspection object.

Japanese Patent No. 5461258

  However, since the conventional magnetic sensors included in the detection head have a sharp directivity in the width direction of the conveyor and are arranged in the width direction, the magnetic sensors are arranged at high density in the width direction of the conveyor. However, there is a problem that it is difficult to improve the accuracy of metal detection.

  Moreover, since the AD converter and the determination unit are connected to each core of the magnetic sensor in the conventional one, the number of signal processing circuits increases depending on the number of magnetic sensors, and the apparatus becomes complicated. there were. This problem has been an obstacle to increase sensitivity by increasing the number of magnetic sensors.

  The present invention has been made to solve the conventional problems, and can improve the sensitivity and accuracy of metal detection, and can reduce the number of signal processing circuits by half compared with the conventional metal. An object is to provide a detector.

  The metal detector according to claim 1 of the present invention is a magnetic means (50) for magnetizing the metal (2) contained in the inspection object (1), and a magnetic field detection for detecting a magnetic field generated by the magnetized metal. Means (61-68) and determination means (81-88) for determining the presence or absence of the metal in the inspection object based on the detection result of the magnetic field detection means, the magnetic field detection means, At least one magnetic sensor (71 to 78) having sharp directivity in the direction perpendicular to the transport surface (24) of the transport path (21) through which the inspection object is transported and arranged in the width direction of the transport path. And a sensor circuit (831) for differentially amplifying and detecting a voltage signal from the magnetic sensor, the magnetic sensor having a longitudinal direction in the vertical direction and a pair of cores arranged in the width direction (733, 734) and the gold wound around each core There has a pair of coils (735, 736) each generating a voltage signal corresponding to the magnetic field generated, a configuration with a.

  With this configuration, in the metal detector according to the first aspect of the present invention, the magnetic sensor is not oriented in the width direction of the transport path as in the prior art, but is sharply directed in the direction perpendicular to the transport surface where higher sensitivity can be achieved. Therefore, it is possible to arrange a larger number of magnetic sensors than before while achieving high sensitivity, and therefore, the arrangement of the cores of the magnetic sensors can be made higher than in the past. As a result, the metal detector according to claim 1 of the present invention can increase the sensitivity and accuracy of metal detection.

  In addition, with this configuration, the metal detector according to claim 1 of the present invention includes a sensor circuit that differentially amplifies and detects a voltage signal from the magnetic sensor, so that a signal processing circuit is provided for each magnetic sensor as in the prior art. The number of signal processing circuits can be halved.

  Therefore, the metal detector according to claim 1 of the present invention can increase the sensitivity and accuracy of metal detection, and can halve the number of signal processing circuits compared to the conventional one.

  In the metal detector according to claim 2 of the present invention, the magnetic sensor applies an alternating current to each core such that the magnetic moment of each core is periodically orthogonal to the longitudinal direction of each core. An orthogonal fluxgate sensor to be supplied is preferable.

In the metal detector according to claim 3 of the present invention, the orthogonal fluxgate sensor is preferably a fundamental wave orthogonal fluxgate sensor in which a direct current is superimposed on an alternating current.

A metal detector according to a fourth aspect of the present invention includes a plurality of the magnetic sensors, and each of the magnetic sensors includes first and second sensor heads (731, 732) each including the pair of cores, The first sensor head of the other magnetic sensor is provided between the first sensor head and the second sensor head of one of the magnetic sensors adjacent to each other in the width direction. The second sensor head of the one magnetic sensor is provided between the first sensor head and the second sensor head.

With this configuration, the metal detector according to claim 4 of the present invention can increase the distance between the first sensor head and the second sensor head, so that the sensitivity in the width direction of the transport path is improved. Can be made.

In the metal detector according to claim 5 of the present invention, the determination means determines the presence / absence of the metal in the inspection object and the position in the width direction based on an output signal of the sensor circuit. have.

With this configuration, the metal detector according to claim 5 of the present invention can determine the presence / absence of the metal in the inspection object and the position in the width direction.

  The present invention can provide a metal detector that can increase the sensitivity and accuracy of metal detection and that has the effect of halving the number of signal processing circuits compared to the prior art. is there.

It is the upper side figure and side sectional drawing of the metal detector in one Embodiment of this invention. It is a figure which shows the front cross section and signal processing circuit of the metal detector in one Embodiment of this invention. It is a block diagram of the detection part of the metal detector in one Embodiment of this invention. It is a figure which shows an example of the sensor head which can be used for the metal detector in one Embodiment of this invention. It is a figure which shows the front cross section and signal processing circuit of the modification of the metal detector in one Embodiment of this invention.

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

  First, the structure of the metal detector 10 in one embodiment of the present invention will be described with reference to FIG. Fig.1 (a) is a top view of the metal detector 10 in this embodiment, FIG.1 (b) is side surface sectional drawing in the segment CC of Fig.1 (a).

  As shown in FIG. 1, the metal detector 10 according to the present embodiment includes a conveyor 20 that conveys the inspection object 1, and an upper detection head 30 and a lower detection head 40 that are provided above and below the conveyor 20. , And a magnetized portion 50 provided on the upstream side of the upper detection head 30 and the lower detection head 40.

  The metal detector 10 includes, for example, a CPU, a ROM, a RAM, and an input / output interface circuit, a non-volatile memory, a hard disk, etc., and a predetermined metal detection control stored in the ROM, the non-volatile memory, the hard disk, etc. According to the program, it is determined whether or not metal is mixed in the inspection object 1.

  The conveyor 20 includes an endless annular conveyance belt 21 that conveys the inspection object 1 in the conveyance direction A, and conveyance rollers 22 and 23 that drive the conveyance belt 21. The conveyor belt 21 has a conveyor surface 24 on which the inspection object 1 is placed. The conveyance belt 21 is an example of a conveyance path.

  The upper detection head 30 includes a plurality of sensor heads 731 and the like arranged in a line in the direction orthogonal to the conveyance direction A, that is, the width direction B of the conveyance belt 21, and the surroundings of the sensor heads 731 And a magnetic shield 31 formed so as to surround.

  The lower detection head 40 is provided so as to face the upper detection head 30. Like the upper detection head 30, the lower detection head 40 includes a plurality of sensor heads 771 arranged in a line in the width direction B of the conveyor belt 21. And a magnetic shield 41 formed so as to surround the periphery of the sensor head 771 and the like (excluding the conveyor 20 side). In the present embodiment, the distance from the conveyance surface 24 of the conveyance belt 21 to the sensor head 731 of the upper detection head 30 and the distance from the conveyance surface 24 of the conveyance belt 21 to the sensor head 771 of the lower detection head 40 are determined. Same length.

  2, which will be described later, the upper detection head 30 includes a plurality of sensor heads 711, 712, 721, 722, 731, 732, 741, and 742. Similarly, the lower detection head 40 includes a plurality of sensor heads 751, 752, 761, 762, 771, 772, 781, 782.

  The magnetizing unit 50 includes a magnet that is provided across the conveying surface 24 of the conveying belt 21 and generates a DC magnetic field in the vertical direction H. When the inspection object 1 includes the metal 2, the metal 2 is magnetized by the magnetized portion 50 and has a predetermined residual magnetization level. That is, the magnetized portion 50 is an example of a magnetizing unit that magnetizes the metal 2 included in the device under test 1. In addition, when magnetizing the metal 2 in the inspection object 1 outside the metal detector 10, the magnetizing unit 50 can be configured not to be provided in the metal detector 10.

  Next, a configuration including a signal processing circuit of the metal detector 10 will be described with reference to FIG. FIG. 2 is a diagram showing a front cross section and a signal processing circuit in the line segment DD of FIG.

  As shown in FIG. 2, the metal detector 10 includes a determination result display unit 69 that displays the result of determining the presence or absence of the metal 2 in the inspection object 1 in the upper detection head 30 and the lower detection head 40. Yes.

  The upper detection head 30 includes four detection units 61 to 64 as an example. The lower detection head 40 includes detection units 65 to 68 at positions facing the detection units 61 to 64, respectively.

  The detectors 61 to 64 are respectively magnetic sensors 71 to 74 that detect a magnetic field from the metal 2 in the inspection object 1 and the metal 2 in the inspection object 1 based on the detection results of the magnetic sensors 71 to 74. Determination units 81 to 84 that determine whether or not there is any. Similarly, detection units 65-68 include magnetic sensors 75-78 and determination units 85-88, respectively. The detection units 61 to 68 are examples of magnetic field detection means.

  The magnetic sensors 71 to 78 are arranged in a line in the width direction B of the transport path. Since these structures are the same, taking the magnetic sensor 73 as an example, the magnetic sensor 73 has a pair of sensor heads 731 and 732 arranged in a line in the width direction B of the transport path. The arrows shown in the sensor heads 731 and 732 indicate the directivity at a certain time for detecting the magnetic field from the metal 2 in the inspection object 1.

  The determination units 81 to 88 determine the presence or absence of the metal 2 in the inspection object 1 based on the detection results of the magnetic sensors 71 to 78, respectively, and output a determination result signal indicating the determination result to the determination result display unit 69. It is supposed to be. The determination units 81 to 88 are an example of a determination unit, and a detailed configuration thereof will be described later. Moreover, the determination parts 81-88 output the intensity | strength signal which shows the intensity | strength of the detection signal from the magnetic sensors 71-78 to the determination result display part 69 so that it may mention later.

  The determination result display unit 69 inputs the determination results from the determination units 81 to 88, and displays the determination results. In addition, the determination result display unit 69 indicates the position of the metal 2 in the inspection object 1 in the width direction B and the vertical direction H of the conveyor belt 21 based on the intensity signals from the determination units 81 to 88, as will be described later. Detected and displayed.

  Next, a detailed configuration of the detection unit 63 as a representative of the detection units 61 to 68 will be described with reference to FIG. FIG. 3 is a configuration diagram of the detection unit 63 shown in FIG.

  As shown in FIG. 3, the detection unit 63 includes a magnetic sensor 73 and a determination unit 83.

  The magnetic sensor 73 includes a pair of sensor heads 731 and 732, a signal generator 737, and a DC power source 738.

  The pair of sensor heads 731 and 732 are arranged in a line in the width direction B of the transport belt 21 as described above, and have a sharp directivity in an orthogonal direction orthogonal to the transport surface 24 as shown in FIG. Yes.

  The sensor head 731 has a core 733 and a coil 735. The sensor head 732 includes a core 734 and a coil 736. Here, the cores 733 and 734 are an example of a pair of cores. The coils 735 and 736 are an example of a pair of coils.

  The cores 733 and 734 are each formed of a U-shaped magnetic wire, for example, an amorphous magnetic wire. The coils 735 and 736 have different winding directions and are connected in anti-series. The lengths of the cores 733 and 734 are optimally about 1.5 to 3 cm. This is because, when the core is lengthened, the resolution can be increased and the directivity can be sharpened, but an insensitive body is generated at the center.

  A modification of the sensor head 731 (or 732) will be described with reference to FIG. Instead of the sensor head 731 shown in FIG. 4A, for example, a sensor head 90 shown in FIG. 4B can be employed. By differentially connecting the two sensor heads 90, the sensor heads 731 and 732 in this embodiment can be used.

  The sensor head 90 includes a core 91 made of, for example, a U-shaped amorphous magnetic wire, insulators 92 and 93 provided on the core 91, and coils 94 and 95 having different winding directions. Similar to the sensor head 711 (or 712), the sensor head 90 has a strong sensitivity to the detected magnetic field in the direction of the arrow in the figure.

  Returning to FIG. 3, the signal generator 737 generates a sine wave signal of 100 kHz, for example, and supplies an exciting current to the cores 733 and 734.

  The DC power source 738 applies a predetermined DC bias voltage to the voltage of the sine wave signal generated by the signal generator 737.

  With this configuration, the magnetic sensor 73 can detect only the component in the orthogonal direction orthogonal to the transport surface 24 out of the magnetic flux of the metal 2 in the inspection object 1. In the present embodiment, the magnetic sensor 73 is composed of an orthogonal fluxgate sensor.

  Here, the fluxgate sensor is a small high-sensitivity sensor that can detect a magnetic field of 10 pT to geomagnetic level in a low frequency band from a static magnetic field without requiring cooling or heating. In a fluxgate sensor, a core that provides an elongated magnetic path for a magnetic field to be detected and a coil wound around the core are basic elements of the sensor head.

  There are two types of fluxgate sensors, namely, 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 detected. Among these, the 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.

  The orthogonal fluxgate sensor has an advantage that the configuration of the sensor head can be simplified because the magnetic permeability can be modulated by passing an alternating current directly through the magnetic wire. In addition, the orthogonal fluxgate sensor superimposes a DC current with an amplitude value or more on the AC excitation current, so that the frequency of the signal voltage induced in the coil is the fundamental frequency of the excitation frequency (in conventional fluxgate sensors). 2 frequency), the circuit is simplified, the sensitivity is increased, and the core noise is suppressed. (Reference: IEEJ Magnetics Study Group: MAG-08-133 “Negative feedback configuration” Operation and Characteristics of Fundamental Wave Type Orthogonal Flux Gate "Ichiro Hamada, Masanori Murakami (Kyushu University)).

  On the other hand, 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, and the parallel type flux gate sensor uses an alternating current used for modulation. Since the excitation magnetic field and the magnetic field to be detected are parallel or anti-parallel, 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.

  The determination unit 83 includes a sensor circuit 831, an ADC (analog / digital converter) 832, and a determination circuit 833.

  The sensor circuit 831 receives voltage signals from the coils 735 and 736 wound around the cores 733 and 734, performs differential amplification and detection, and outputs them to the ADC 832. The sensor circuit 831 is provided in front of the ADC 832, and is configured to directly amplify and detect the voltage signals from the coils 735 and 736, so that a relatively large differential amplified signal can be acquired. This is preferable. In addition, since the metal detector 10 includes the sensor circuit 831, it can cancel an external constant magnetic field, for example, geomagnetism, and is not easily affected by this type of external magnetic field. As a result, the metal detector 10 can make the configuration of the magnetic shields 31 and 41 simpler than before, and can reduce the cost. Specifically, according to the examination results, the metal detector 10 has conventionally required about 3 to 4 magnetic plates, but it can be reduced to one.

  The ADC 832 converts the input analog voltage signal into a digital value and outputs the digital value to the determination circuit 833.

  The determination circuit 833 compares the input voltage signal with a predetermined threshold voltage, and determines a determination result signal indicating whether or not the metal 2 is mixed in the inspection object 1 based on the comparison result. The data is output to the display unit 69. For example, when the input signal input is higher than the threshold voltage, the determination circuit 833 outputs a determination result signal indicating that the metal 2 is mixed in the inspection object 1. In addition, the determination circuit 833 outputs an intensity signal indicating the intensity of the detection signal from the magnetic sensor 73 to the determination result display unit 69.

  The determination result display unit 69 displays a determination result as to whether or not the metal 2 is mixed in the inspection object 1 based on the determination result signal from the determination circuit 833. Further, the determination result display unit 69 detects and displays the position in the width direction B of the metal 2 in the inspection object 1 based on the intensity signal from the determination circuit 833.

  Next, the operation of the metal detector 10 in this embodiment will be described.

  When the inspection object 1 passes through the magnetized portion 50 shown in FIG. 1, when the metal 2 is mixed in the inspection object 1, the metal 2 is magnetized and has a predetermined residual magnetization level. Become.

  When the inspection object 1 including the magnetized metal 2 passes between the upper detection head 30 and the lower detection head 40, magnetic fields from the metal 2 are detected by the magnetic sensors 71 to 78, and the magnetic sensors 71 to 78 are detected. The output of each sensor circuit 831 etc. connected to fluctuates.

  For example, in the state shown in FIG. 2, the strongest detection of the magnetic field from the metal 2 is the detection unit 63 having the magnetic sensor 73 at the position closest to the metal 2, followed by the detection units 62, 67, 66,... In this case, for example, in the detection unit 63, the output of the sensor circuit 831 is converted from an analog value to a digital value by the ADC 832 and input to the determination circuit 833. The determination circuit 833 compares the output of the ADC 832 with a determination threshold value. If the determination threshold value is exceeded, a determination result signal indicating that the metal 2 is mixed in the inspection object 1 is displayed in the determination result display unit 69. Output. As a result, the determination result display unit 69 can display that the metal 2 is mixed in the inspection object 1.

  In addition, since each intensity signal corresponding to the strength of the magnetic field of the metal 2 is output from the determination circuits 833 of the detection units 61 to 68 to the determination result display unit 69, in the state shown in FIG. The intensity signal from the determination circuit 833 of the unit 63 is the strongest, followed by the detection units 62, 67, 66,. Therefore, the determination result display unit 69 can calculate the position of the metal 2 in the inspection object 1 in the width direction B of the transport belt 21 from the difference or ratio of these intensity signals and display the result. Further, the determination result display unit 69 can calculate the position of the metal 2 in the inspection object 1 in the vertical direction H from the difference or ratio of these intensity signals and display the result.

  As described above, in the metal detector 10 according to the present embodiment, the magnetic sensors 71 to 78 are not in the width direction of the transport belt 21 as in the prior art, but in the direction perpendicular to the transport surface 24 where higher sensitivity can be achieved. Therefore, it is possible to arrange a larger number of magnetic sensors than in the past while achieving high sensitivity, so that the arrangement of the cores of the magnetic sensor can be made higher than in the past. As a result, the metal detector 10 according to the present embodiment can increase the sensitivity and accuracy of metal detection.

  Moreover, since the metal detector 10 in the present embodiment includes the sensor circuit 831 and the like that differentially amplifies and detects the voltage signal from the magnetic sensor 73 and the like, it is necessary to include a signal processing circuit for each magnetic sensor as in the past. The number of signal processing circuits can be halved.

  Therefore, the metal detector 10 in the present embodiment can increase the sensitivity and accuracy of metal detection, and can halve the number of signal processing circuits as compared with the prior art.

(Modification)
Next, a modification of this embodiment will be described with reference to FIG.

  As shown in FIG. 5, the metal detector 11 is obtained by changing the position of the sensor head with respect to the above-described embodiment. As an example, the configuration of the detection units 63 and 64 that are adjacent to each other will be described.

  The detection unit 63 includes a magnetic sensor 73, and the magnetic sensor 73 includes sensor heads 731 and 732. The detection unit 64 includes a magnetic sensor 74, and the magnetic sensor 74 includes sensor heads 741 and 742.

  When the magnetic sensor 73 is called one magnetic sensor and the magnetic sensor 74 is called the other magnetic sensor, the sensor head 741 of the other magnetic sensor 74 is provided between the sensor head 731 and the sensor head 732 of one magnetic sensor 73. The sensor head 732 of one magnetic sensor 73 is provided between the sensor head 741 and the sensor head 742 of the other magnetic sensor 74. Here, the sensor head 731 and the sensor head 741 are examples of a first sensor head, and the sensor head 732 and the sensor head 742 are examples of a second sensor head. The magnetic sensors 71 and 72, the magnetic sensors 75 and 76, and the magnetic sensors 77 and 78 have the same configuration.

  With this configuration, the metal detector 11 can make the distance between the sensor head 731 and the sensor head 732 and the distance between the sensor head 741 and the sensor head 742 longer than in the above-described embodiment. The sensitivity in the width direction can be improved.

  As described above, the metal detector according to the present invention can increase the sensitivity and accuracy of metal detection, and has the effect that the number of signal processing circuits can be halved as compared with the prior art. It is useful as a metal detector for detecting the presence or absence of metal in a test object such as food or clothing.

DESCRIPTION OF SYMBOLS 1 Inspection object 2 Metal 10, 11 Metal detector 21 Conveyance belt (conveyance path)
24 Conveying surface 30 Upper detection head 31 Magnetic shield 40 Lower detection head 41 Magnetic shield 50 Magnetized portion (magnetizing means)
61-68 detection part (magnetic field detection means)
71-78 Magnetic sensor (orthogonal fluxgate sensor, fundamental wave orthogonal fluxgate sensor)
81-88 determination part (determination means)
90 Sensor heads 711, 712, 721, 722, 731, 732, 741, 742 Sensor heads 733, 734 Core (a pair of cores)
735, 736 Coils (a pair of coils)
737 Signal generator 738 DC power supply 751, 752, 761, 762, 771, 772, 781, 782 Sensor head 831 Sensor circuit 833 Determination circuit

Claims (5)

Magnetizing means (50) for magnetizing the metal (2) contained in the object to be inspected (1);
Magnetic field detection means (61-68) for detecting a magnetic field generated by the magnetized metal,
Determination means (81-88) for determining the presence or absence of the metal in the inspection object based on the detection result of the magnetic field detection means;
With
The magnetic field detection means includes
At least one magnetic sensor (71 to 78) having sharp directivity in a direction perpendicular to the transport surface (24) of the transport path (21) through which the inspection object is transported and arranged in the width direction of the transport path. )When,
A sensor circuit (831) for differentially amplifying and detecting a voltage signal from the magnetic sensor;
With
The magnetic sensor is
A pair of cores (733, 734) having a longitudinal direction in the vertical direction and arranged in the width direction;
A pair of coils (735, 736) each generating a voltage signal corresponding to the magnetic field generated by the metal wound around each core;
A metal detector characterized by comprising:   The magnetic sensor is an orthogonal fluxgate sensor that supplies an alternating current to each core so that the magnetic moment of each core is periodically orthogonal to the longitudinal direction of each core. The metal detector according to claim 1. The metal detector according to claim 2, wherein the orthogonal fluxgate sensor is a fundamental wave orthogonal fluxgate sensor in which a direct current is superimposed on an alternating current . A plurality of the magnetic sensors;
Each magnetic sensor includes first and second sensor heads (731, 732) each including the pair of cores,
The first sensor head of the other magnetic sensor is provided between the first sensor head and the second sensor head of one of the magnetic sensors adjacent to each other in the width direction,
The second sensor head of the one magnetic sensor is provided between the first sensor head and the second sensor head of the other magnetic sensor. 4. The metal detector according to any one of up to 3. The determination means of claims 1 to 4, characterized in that on the basis of the output signal of the sensor circuit is to determine the position of presence and the width direction of the metal of the object to be inspected in The metal detector according to any one of claims.

Images