JP2005227029A - Metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sharply reduce the level of noise included in combined detection signals obtained by together combining detection signals of respective detection sensors 11 to 14. <P>SOLUTION: A plurality of detection sensors 11 and 12 are disposed in a conveyance direction while one or more detection sensors 13 and 14 are disposed via conveyance paths for one or more detection sensors among the plurality of detection sensors. A connection selection part 16 selects a connection state between detection sensors for obtaining the combined detection signal and outputs one combined detection signal among a plurality of kinds of combined detection signals. In a state that a body 1 under test is kept from being conveyed to a conveyance mechanism 2, that is, on condition comprising only an external electromagnetic noise environment condition, a connection state for minimizing the signal level of the combined detection signal is set in the selection part 16. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal detection apparatus that detects metal as a foreign substance contained in a subject such as food.

  In general, a metal detection device for detecting metal as a foreign substance contained in food is disposed in a quality inspection line of a food factory that manufactures and ships confectionery, meat, prepared dishes, lactic acid beverages, and the like. This metal detection apparatus is configured as shown in FIG. 11, for example (see Patent Document 1).

  In FIG. 11, for example, the metal contained in the subject 1 transported on the conveyor 2 is DC magnetized upstream of the transport direction indicated by the arrow of the conveyor 2 as a transport mechanism for transporting the subject 1 made of food. A magnetizer 4 in which the exciting coil 3 is incorporated is provided. A detection head 7 in which a pair of magnetic sensors 5 and 6 each including a detection coil that is disposed apart from each other in the transport direction is disposed downstream of the conveyor 2 in the transport direction. The pair of magnetic sensors 5 and 6 are differentially connected.

In the magnetic sensors 5 and 6 including the detection coils, if the subject 1 transported in the vicinity of the magnetic sensors 5 and 6 contains magnetized metal, a current due to an electromotive force flows through the detection coils. The detection signals d ₁ and d _{2 of the} magnetic sensors 5 and 6 are obtained. Since the magnetic sensors 5 and 6 are differentially connected, a differential detection signal Δd of the detection signals d ₁ and d ₂ is sent from the detection head 7 to the control unit 8.

Δd = d ₁ −d ₂
The control unit 8 sends a direct current excitation current to the magnetizer 4. Further, when the input difference detection signal Δd exceeds a prestored threshold value, the control unit 8 determines that metal exists in the subject 1 and outputs a metal detection signal.

Note that the pair of magnetic sensors 5 and 6 disposed apart from each other in the transport direction do not detect the metal of the same subject 1 at the same timing, and the detection signal d _{1 of the} magnetic sensors 5 and 6. , D ₂ are assumed to contain substantially the same level of noise, the difference detection signal Δd between the detection signals d ₁ , d ₂ is adopted, so that the difference detection signal sent from the detection head 7 to the control unit 8 is used. The noise level included in Δd can be reduced.
Japanese Patent Laid-Open No. 2003-66156

  However, the metal detector shown in FIG. 11 still has the following problems that should be solved.

  That is, as described above, this metal detection device is generally incorporated in a quality inspection line in a food factory. In addition to the metal detection device, the quality inspection line carries food as the subject 1 to the metal detection device, an electric motor that drives a number of conveyors that carry food from the metal detection device, and has been inspected. Many electrical devices such as packing devices for packing foods are installed.

In the operating state, these electric devices generate various electromagnetic noises on a regular basis or suddenly when the power is turned on or when the power is turned off. Electromagnetic noise generated by this electric device is mixed in the detection signals d ₁ and d ₂ of the magnetic sensors 5 and 6 of the detection head 7.

In this case, the noise level included in the detection signals d ₁ and d ₂ of the magnetic sensors 5 and 6 of the metal detector is large depending on the installation location of each electric device, the level and type of electromagnetic noise, and the direction of arrival of the electromagnetic noise. Variations occur.

Therefore, as in the metal detector shown in FIG. 11, the magnetic sensors 5 and 6 that are spaced apart from each other in the transport direction are differentially connected, and the difference detection signal Δd of the detection signals d ₁ and d ₂ is employed. However, the noise level included in the difference detection signal Δd cannot be sufficiently reduced.

  In general, the detection level (detection sensitivity) of metal detection in each of the magnetic sensors 5 and 6 is low, so that the detection level (detection sensitivity) of metal detection in the difference detection signal Δd is not sufficient.

  The present invention has been made in view of such circumstances, and the noise contained in the combined detection signal obtained by synthesizing the detection signal of each detection sensor that detects the metal contained in the subject, regardless of the external electromagnetic noise environment. An object of the present invention is to provide a metal detection device capable of greatly reducing the level and sufficiently ensuring the detection level (detection sensitivity) of metal detection as required, and improving the reliability and detection accuracy of metal detection.

  In the metal detection apparatus of the present invention, a transport mechanism that transports the subject, and a plurality of detection sensors that are disposed apart from each other in the transport direction of the transport path in the transport mechanism and detect the metal contained in the subject. One or more detection sensors which are arranged at positions facing one or more detection sensors of the plurality of detection sensors via the conveyance path and detect metal contained in the subject, and each detection A determination control unit that determines the presence or absence of metal in the subject based on a combined detection signal obtained by combining the detection signals of the sensors.

  And the determination control part of this metal detection apparatus switches the connection state between the detection sensors for obtaining the composite detection signal, and outputs a composite detection signal of a plurality of kinds of composite detection signals. In a state in which the subject is not transported to the transport mechanism, the connection state of each detection sensor in the connection switching unit is switched, and the signal level of the combined detection signal in each connection state is detected, so that the connection state with the minimum signal level is achieved. A connection state selection unit that selects and sets the connection switching unit, and a combined detection signal that is output from the connection switching unit that is in the connection state set by the connection state selection unit in a state where the subject is transported to the transport mechanism Determination means for determining the presence or absence of metal in the subject based on the above.

  In the metal detection device configured as described above, a plurality of detection sensors are arranged in the transport direction, and at least one of the plurality of detection sensors is detected via the transport path. These detection sensors are arranged. The connection switching unit switches a connection state between the detection sensors for obtaining a combined detection signal, and outputs one combined detection signal among a plurality of types of combined detection signals.

  Then, a connection state in which the signal level of the combined detection signal is minimum is set in the connection switching unit in a state in which the subject is not transported by the transport mechanism, that is, only in an external electromagnetic noise environment condition.

  Therefore, in this connection state, the noise level of the combined detection signal when the metal contained in the subject is detected by each detection sensor can be greatly reduced.

  In another aspect of the invention, the connection switching unit of the metal detector of the invention described above is a detection for obtaining a differential signal of detection signals of at least the detection sensors disposed at positions facing each other via the transport path. The differential connection state of the sensors, the addition connection state of the detection sensors for obtaining the addition signal of the detection signals of the respective detection sensors disposed at positions facing each other through the conveyance path, and the separation direction in the conveyance direction of the conveyance path The differential connection state of the detection sensor for obtaining the differential signal of the detection signal of each detection sensor arranged in this manner is switched.

  In the metal detection apparatus configured as described above, in the differential connection state in which the differential signal of the detection signal of each detection sensor is obtained, the noise level mainly included in the combined detection signal is reduced. In addition, in the addition connection state in which the addition signal of the detection signal of each detection sensor is obtained, the detection level (detection sensitivity) of metal detection mainly included in the composite detection signal is increased.

  Therefore, in an electromagnetic noise environment where the noise level is high, the differential connection state is selected to reduce the noise level included in the composite detection signal to improve the reliability of metal detection, and in the electromagnetic noise environment where the noise level is low, It is possible to improve the metal detection accuracy by selecting the addition connection state and increasing the detection level (detection sensitivity) of the metal detection included in the composite detection signal.

  In another aspect of the present invention, the metal detector according to the present invention includes a magnetizer that magnetizes a metal contained in a subject being transported by a transport mechanism. The detection sensor is a magnetic sensor that detects magnetized metal contained in the object being transported.

  Still another invention is the above-described metal detection device according to the invention, further comprising one common magnetic field generation device for forming an equal magnetic field at the position of each detection sensor in the plurality of detection sensors. The detection sensor detects the metal contained in the object being transported based on the magnetic field formed by the common magnetic field generator.

  In the metal detection device of the present invention, regardless of the external electromagnetic noise environment, the noise level included in the combined detection signal obtained by combining the detection signals of the detection sensors that detect the metal included in the subject can be greatly reduced, In addition, the detection level (detection sensitivity) of metal detection can be sufficiently secured as required, and the reliability and detection accuracy of metal detection can be improved.

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

(First embodiment)
FIG. 1 is a schematic diagram showing a schematic configuration of a metal detector according to the first embodiment of the present invention. The same parts as those of the conventional metal detector shown in FIG. 11 are denoted by the same reference numerals, and detailed description of the overlapping parts is omitted.

  For example, an exciting coil for DC magnetizing the metal contained in the subject 1 conveyed on the conveyor 2 is incorporated upstream of the conveying direction indicated by the arrow of the conveyor 2 as a conveying mechanism for conveying the subject 1 made of food. A magnetizer 4 is provided. A direct current excitation current is supplied to the magnetizer 4 from an excitation power source 10.

  A pair of magnetic sensors 11 and 12 composed of detection coils are disposed downstream of the conveyor 2 in the conveying direction and at a lower position of the conveyor 2 and spaced apart from each other in the conveying direction. Magnetic sensors 13 and 14 are disposed at positions facing the magnetic sensors 11 and 12 via the conveyor 2.

  FIG. 2 is a top view of the main part of the metal detection device. Each of the magnetic sensors 11, 12, 13, and 14 including the magnetizer 4 in which the excitation coil is incorporated and the detection coil covers a range wider than the width of the conveyor 2 that conveys the subject 1.

In each of the magnetic sensors 11, 12, 13, and 14 including the detection coils, if the subject 1 transported in the vicinity of the magnetic sensors 11, 12, 13, and 14 contains magnetized metal, A current due to electric power flows, and this current becomes detection signals A, B, C and D of the magnetic sensors 11, 12, 13 and 14. Each coil terminal (A ₁ , A ₂ ), (B ₁ , B ₂ ), (C ₁ , C ₂ ), (D ₁ , D ₂ ) of each magnetic sensor 11, 12, 13, 14 is, for example, from a computer Connected to each terminal of the connection switching unit 16 in the determination control unit 15.

  In the determination control unit 15, in addition to the connection switching unit 16, a reception unit 17 that receives the composite detection signal s output from the connection switching unit 16, a connection state selection unit 18, a comparison unit 19, and a threshold memory 20. A display unit 21 and an output terminal 22 are provided.

  The connection switching unit 16 switches the connection state between the magnetic sensors 11, 12, 13, and 14 and outputs one combined detection signal s among a plurality of types of combined detection signals. That is, the combined detection signals s obtained by combining the detection signals A, B, C, and D of the magnetic sensors 11, 12, 13, and 14 are different depending on the connection state between the magnetic sensors 11, 12, 13, and 14. It becomes a composite form. The connection switching unit 16 outputs one composite detection signal s corresponding to the connection state. In this embodiment, four types of connection states can be switched.

  The receiving unit 17 amplifies the combined detection signal s output from the connection switching unit 16, performs A / D conversion, and sends it to the connection state selection unit 18 and the comparison unit 19 as a digital combined detection signal s.

  FIG. 3 is a block diagram showing a schematic configuration of the connection state selection unit 18. In the connection state selection unit 18, a connection state memory 23, a connection state instruction unit 24, a signal level detection unit 25, a signal level memory 26, and a connection state determination unit 27 are provided.

  In the connection state memory 23, as shown in FIG. 4, four types of connection states No. 1 to No. 4 in the connection switching unit 16 are detected signals A, B, C, It is expressed and stored using D.

For example, in the connection state indicated by [(AC)-(BD)] of No. 1, the magnetic sensors (11, 13) and (12, 14) that face each other are differentially connected and differentially connected. The pair of magnetic sensors (11, 13) and (12, 14) in the transport direction is further differentially connected. As a result, the combined detection signal s ₁ in the connection state of No. ₁ is
s ₁ = (AC)-(BD)
It becomes.

In addition, the connection state indicated by [(A + C) − (B + D)] of No. 2 is such that the magnetic sensors (11, 13) and (12, 14) facing each other are added and connected, and the magnetism in the transport direction is added and connected. The pair of sensors (11, 13) and (12, 14) is differentially connected. As a result, the combined detection signal s ₂ in the connection state of No. ₂ is
s ₂ = (A + C) − (B + D)
It becomes.

In addition, the connection state indicated by [(AC) + (BD)] of No. 3 is obtained by differentially connecting the magnetic sensors (11, 13) and (12, 14) opposed to each other in the vertical direction. A set of magnetic sensors (11, 13) and (12, 14) in the transport direction is added and connected. As a result, the combined detection signal s ₃ in the connection state of No. ₃ is
s ₃ = (AC) + (BD)
It becomes.

Further, the connection state indicated by [(A + C) + (B + D)] of No. 4 is such that the magnetic sensors (11, 13) and (12, 14) facing each other are added and connected, and the magnetism in the transport direction is added and connected. A set of sensors (11, 13) and (12, 14) is further added and connected. As a result, the combined detection signal s ₄ in the connection state of No. ₄ is
s ₄ = (A + C) + (B + D)
It becomes.

  Here, with reference to FIG. 5, the basic principle of removing electromagnetic noise input from the outside using a plurality of magnetic sensors will be described. As shown in FIG. 5, three-axis coordinates (X, Y, Z) having the origin at the center of four magnetic sensors 11, 13, 12, 14 are assumed. The conveyance direction of the subject 1 on the conveyor 2 is parallel to the X axis.

  First, assuming that the combined detection signal is taken out from the two magnetic sensors, it can be explained as follows.

  When there is a noise source on the XY plane, the effective connection state is the differential connection state (detection signal A−detection signal C) of the magnetic sensors 11 and 13 equidistant from the noise source, and the magnetic sensors 12 and 14. The differential connection state (detection signal B-detection signal D).

  When there is a noise source on the YZ plane, the effective connection state is the differential connection state (detection signal A−detection signal B) of the magnetic sensors 11 and 12 equidistant from the noise source, and the magnetic sensors 13 and 14. The differential connection state (detection signal C-detection signal D).

  When there is a noise source on the ZX plane, the effective connection state differs depending on the position of the noise source. For example, if there is a noise source at point E in FIG. 5, selecting two magnetic sensors with a small distance difference between point E and the magnetic sensor and taking out a differential signal as a differential connection state cancels electromagnetic noise. The best way to do it. Here, since the differential connection state of the magnetic sensors 12 and 14 is the best, the differential connection state (detection signal A−detection signal C) of the magnetic sensors 11 and 13 and the differential connection state of the magnetic sensors 12 and 14. Noise removal is performed using (detection signal B−detection signal D).

Next, a case where it is effective to obtain a combined detection signal from the combined detection signal described above will be described.
If there is a noise source at point F in FIG. 5, the differential connection state (detection signal A−detection signal C) of the magnetic sensors 11 and 13 and the differential connection of the magnetic sensors 12 and 14 are the same as described above. By adopting the state (detection signal B-detection signal D), two combined detection signals (AC) and (BD) are taken out.

  Since the noise source is slightly deviated from the XY plane, noise components remain in the respective composite detection signals (AC) and (BD). Therefore, the two combined detection signals (AC) and (BD) thus obtained are further connected in a differential connection state to obtain a combined detection signal [(AC)-(BD)]. Thus, the electromagnetic noise component can be further reduced.

  FIG. 6 shows the differential connection state and addition connection state of the magnetic sensors 11 and 13 facing each other and the magnetic sensor 11 spaced apart in the transport direction, which are created based on the basic principle of electromagnetic noise removal described with reference to FIG. The detection level (detection sensitivity) of the metal detection of the combined detection signal s ′ in the differential connection state and the addition connection state, noise resistance against electromagnetic noise entering from the transport direction (X direction), and entering from the vertical direction (Y direction) It is a figure which shows each grade of the noise tolerance with respect to the electromagnetic noise to do.

  The detection level (detection sensitivity) of metal detection is most advantageous in the addition connection state of the magnetic sensors 11 and 13 that face each other and detect the metal at the same timing with the same timing. In addition, with regard to noise resistance against electromagnetic noise entering from the vertical direction (Y direction), the differential connection state of the magnetic sensors 11 and 12 that are separated in the transport direction is most advantageous. Furthermore, with regard to noise resistance against electromagnetic noise that enters from the transport direction (X direction), the differential connection state of the magnetic sensors 11 and 13 that face each other is most advantageous.

  Since the probability that the metal as a foreign substance existing in the subject 1 is accurately located at the intermediate position of the magnetic sensors 11 and 13 is very small, the combined detection signal s ′ of the differential connection state of the magnetic sensors 11 and 13 is used. Signals due to metal detection always appear.

  As described above, the optimum connection state of each of the magnetic sensors 11, 12, 13, and 14 can be selected according to the required detection level (detection sensitivity) of metal detection and the external electromagnetic noise environment.

The connection state selection unit 18 in FIG. 3 activates the connection state instruction unit 24 in a state where the subject 1 is not transported to the conveyor 2 in a state where the power of the metal detection apparatus is turned on, and No1 in the connection state memory 23. The connection states of No. 4 to No. 4 are sequentially read out and sequentially transmitted to the connection switching unit 16. The connection switching unit 16 sequentially realizes the connection states No. _{1 to} No. ₄ of the magnetic sensors 11, 12, 13 and 14, and sequentially outputs the combined detection signals s _{1 to} s ₄ corresponding to the connection states No. _{1 to} No ₄ . Send to receiver 17.

The signal level detection unit 25 detects the signal level of each of the combined detection signals s _{1 to} s ₄ sequentially output from the reception unit 17 and writes it in the signal level memory 26. The connection state determining unit 27, the signal level of the signal level of each joint detection signals s ₁ ~s ₄ written in the signal level memory 26 selects a connection state of the smallest synthetic detection signal s ₁ ~s ₄ To the connection switching unit 16. Further, the connection state determination unit 27 sends the determined connection state to the threshold value memory 20.

The signal levels of the combined detection signals s _{1 to} s ₄ at the time of detecting the same metal in each connection state of No. _{1 to} No. ₄ are different. Therefore, the threshold value memory 20 stores a plurality of threshold values corresponding to the connection states No. 1 to No. 4. Then, the threshold value memory 20 applies a threshold value corresponding to the determined connection state to the comparison unit 19.
This completes the measurement preparation process when the metal detector is powered on.

  The comparison unit 19 serving as a determination unit outputs the combined detection signal output from the connection switching unit 16 via the receiving unit 17 in a state where the subject 1 is transported to the conveyor 2 after the measurement preparation process described above is completed. When the signal level of the combined detection signal s exceeds the threshold value by comparing the signal level of s with the threshold value, it is determined that metal is present in the subject 1 and displayed on the display unit 21, and the output terminal A metal detection signal is output to 22.

  In the metal detection device of the first embodiment configured as described above, each magnetic field in which the combined detection signal s becomes the smallest in accordance with the external electromagnetic noise environment in the measurement preparation stage in the metal detection device after turning on the power. The connection states of the sensors 11, 12, 13, 14 are automatically selected and set in the connection switching unit 16.

  Therefore, it is included in the combined detection signal s obtained by combining the detection signals A, B, C, and D of the detection sensors 11, 12, 13, and 14 that detect the metal included in the subject 1 regardless of the external electromagnetic noise environment. Noise level can be greatly reduced, and the reliability of metal detection can be improved.

The present invention is not limited to the first embodiment described above.
In the measurement preparation stage in the metal detection apparatus after turning on the power, the signal level of each of the combined detection signals s _{1 to} s ₄ written in the signal level memory 26 is displayed on the display unit 21, which is optimal for the operator. It is also possible to add a function that allows the user to select a manual setting method that allows the connection switching unit 16 to manually set the connection state.

In this case, the operator observes the signal level of each of the combined detection signals s _{1 to} s ₄ displayed on the display unit 21 and selects, for example, the No1 differential connection state in an electromagnetic noise environment with a high noise level. Thus, the noise level included in the combined detection signal s is reduced to improve the reliability of metal detection. In an electromagnetic noise environment where the noise level is low, for example, the addition connection state of No. 2 is selected and included in the combined detection signal s. It is possible to improve the metal detection accuracy by increasing the detection level (detection sensitivity) of metal detection.

(Second Embodiment)
FIG. 7 is a schematic diagram showing a schematic configuration of a metal detection apparatus according to the second embodiment of the present invention. The same parts as those of the metal detector according to the second embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description of the overlapping parts is omitted.

In the metal detection device of the second embodiment, three magnetic sensors 11, 12, and 13 are incorporated. The coil terminals (A ₁ , A ₂ ), (B ₁ , B ₂ ), (C ₁ , C ₂ ) of the three magnetic sensors 11, 12, 13 are connected to the connection switching unit 16a in the determination control unit 15a. Connected to each terminal.

In the determination control unit 15a, a connection switching unit 16a, a signal selection unit 31 for selecting each of the combined detection signals s ₅ , s ₆ and s ₇ output from the connection switching unit 16a, a connection state selection unit 18a, and a comparison unit 19 A threshold memory 20, a display unit 21, and an output terminal 22 are provided.

The connection switching unit 16a switches the connection state between the magnetic sensors 11, 12, and 13 and outputs three types of combined detection signals s ₅ , s ₆ , and s _{7 shown} in FIG. The connection state in FIG. 8A is a connection state of No5 in which the magnetic sensors 11 and 13 are in the differential connection state, and the combined detection signal s ₅ is s ₅ = A−C. The connection state of FIG. 8B is a connection state of No. 6 in which the magnetic sensors 11 and 12 are in the differential connection state, and the combined detection signal s ₆ is s ₆ = A−B. Further, the connection state of FIG. 8C is a connection state of No. 7 in which the magnetic sensors 11 and 13 are in the addition connection state, and the combined detection signal s ₇ is s ₇ = A + C.

The connection state selection unit 18a has the lowest signal level among the three types of combination detection signals s ₅ , s ₆ , and s ₇ from the connection switching unit 16a in a state in which the subject 1 is not conveyed to the conveyor 2. A signal is selected and this selection information is sent to the signal selection unit 31. The signal selection unit 31 sends one synthesis detection signal s selected from the three types of synthesis detection signals s ₅ , s ₆ , and s ₇ to the next comparison unit 19.

In addition, the connection state selection unit 18 a sends the connection state corresponding to the selected composite detection signal s to the threshold value memory 20. The threshold value memory 20 stores a plurality of threshold values corresponding to the connection states No. 5 to No. 7. Then, the threshold memory 20 applies a threshold corresponding to the selected connection state to the comparison unit 19. Finally, the connection state selection unit 18a sets the selected connection state in the connection switching unit 16a.
This completes the measurement preparation process when the metal detector is powered on.

  The comparison unit 19 completes the measurement preparation process described above, and then outputs a single composite detection signal s output via the connection switching unit 16a and the signal selection unit 31 in a state where the subject 1 is transported to the conveyor 2. When the signal level of the combined detection signal s exceeds the threshold value, it is determined that metal is present in the subject 1 and displayed on the display unit 21 and the output terminal 22. The metal detection signal is output to.

  A state in which magnetic field noise input from the outside is efficiently removed in the metal detection device of the second embodiment configured as described above will be described with reference to FIG.

As shown in FIG. 9A, when the electromagnetic noise 32 having the waveform shown in the figure is input from the upstream side in the conveying direction of the conveyor 2, the detection of the magnetic sensors 11 and 13 is performed as shown in FIG. The noise waveforms of signals A and C are almost equal. The noise waveform of the detection signal B of the magnetic sensor 12 is smaller than the detection signals A and C of the magnetic sensors 11 and 13. Therefore, in this case, the connection state of the connection state No5 (joint detection signal s ₅ = A-C) to the magnetic sensor 11, 13 and the differential connection state, more effectively compared to other connection state No6, No7 Magnetic field noise is removed.

On the other hand, as shown in FIG. 9A, when the electromagnetic noise 33 having the illustrated waveform is input from the lower side of the conveyor 2, as shown in FIG. 9C, the detection signals of the magnetic sensors 11 and 12 are detected. The noise waveforms of A and B are almost equal. The noise waveform of the detection signal C of the magnetic sensor 13 is smaller than the detection signals A and B of the magnetic sensors 11 and 12. Therefore, in this case, the connection state of connection state No 6 (combined detection signal s ₆ = AB) in which the magnetic sensors 11 and 12 are in the differential connection state is more effective than the other connection states No 5 and No 7. Magnetic field noise is removed.

The present invention is not limited to the above-described embodiments.
For example, as shown in FIG. 10A, a magnetic field generator 34 having a substantially U-shape is disposed at an intermediate position between the magnetic sensors 11 (13) and 12 (14) spaced apart in the transport direction. It is also possible. As shown in FIG. 10B, the distances from the magnetic field center (magnetic field center 35) formed by the magnetic field generator 34 to the magnetic sensors 11, 12, 13, and 14 are set equal. . Accordingly, the magnetic field strengths at the positions of the magnetic sensors 11, 12, 13, and 14 are equal to each other.

  The magnetic field generator 34 generates an alternating magnetic field or a direct magnetic field. Each of the magnetic sensors 11, 12, 13, and 14 is formed of, for example, a reception coil. When the subject 1 containing metal is conveyed on the conveyor 2, the current flowing through the reception coil due to the presence of this metal. Are detected and output as detection signals A, B, C, and D.

  When the magnetic field generated by the magnetic field generator 34 is an alternating magnetic field, a magnetic metal such as iron and a nonmagnetic metal such as aluminum can be detected. When the magnetic field generated by the magnetic field generator 34 is a direct current magnetic field, the magnetic metal Can only be detected. The magnetic field generated by the magnetic field generator 34 can be selected from an AC magnetic field and a DC magnetic field depending on the material of the subject 1.

  Further, the magnetic field generator 34 may be integrated with each of the magnetic sensors 11, 12, 13, and 14 as shown in FIG.

  Furthermore, the conveyor 2 that is the transport path of the subject 1 may be cylindrical when the subject 1 has fluidity. There may be a magnetic sensor in the middle of the sample 1 dropping. Thus, the conveyance path is not limited to the conveyor 2.

The schematic diagram which shows schematic structure of the metal detection apparatus concerning 1st Embodiment of this invention. Top view of the main part of the metal detector according to the same embodiment The block diagram which shows schematic structure of the connection state selection part of the metal detection apparatus concerning the embodiment The figure which shows the memory content of the connection state memory built in the connection state selection part of the metal detection apparatus The figure which shows the basic principle by which the electromagnetic noise input from the outside is removed using a plurality of magnetic sensors in the metal detection device The figure which shows the relationship between each connection state of the magnetic sensor of the same metal detection apparatus, the detection level (detection sensitivity) of metal detection, and each degree of noise resistance against electromagnetic noise The schematic diagram which shows schematic structure of the metal detection apparatus concerning 2nd Embodiment of this invention. The figure which shows the connection state implement | achieved in the connection switching part of the metal detection apparatus Waveform diagram showing the state where electromagnetic noise of the metal detector is removed The schematic diagram which shows the principal part of the metal detection apparatus concerning other embodiment of this invention. Schematic diagram showing the schematic configuration of a conventional metal detector

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Subject, 2 ... Conveyor, 4 ... Magnetizer, 10 ... Excitation power supply, 11-14 ... Magnetic sensor, 15, 15a ... Determination control part, 16, 16a ... Connection switching part, 17 ... Receiving part, 18, 18a Connection state selection unit, 19 Comparison unit, 20 Threshold memory, 21 Display unit, 22 Output terminal, 23 Connection state memory, 24 Connection state indication unit, 25 Signal level detection unit, 26 Signal level memory, 27... Connection state determination unit, 31... Signal selection unit, 34.

Claims (4)

A transport mechanism (2) that transports the subject (1) and a plurality of detection sensors (11, 11) that are spaced apart from each other in the transport direction of the transport path in the transport mechanism and detect the metal contained in the subject. 12) and one or more detections arranged to face one or more detection sensors of the plurality of detection sensors via the conveyance path and detect a metal contained in the subject. A sensor (13, 14) and a determination control unit (15) for determining the presence or absence of metal in the subject based on a combined detection signal obtained by combining the detection signals of the detection sensors (11, 12, 13, 14). A metal detection device comprising:
The determination control unit
A connection switching unit (16) for switching a connection state between the detection sensors for obtaining the combined detection signal and outputting one combined detection signal among a plurality of types of combined detection signals;
In a state where the subject is not transported to the transport mechanism, the connection state of each detection sensor in the connection switching unit is switched, and the signal level of the combined detection signal in each connection state is detected, and the connection state with the minimum signal level is determined. Connection state selection means (18) for selecting and setting in the connection switching section;
In the state where the subject is transported to the transport mechanism, the presence / absence of metal in the subject is determined based on the composite detection signal output from the connection switching unit which is the connection state set by the connection state selection means. A metal detection device comprising a determination means (19).   The connection switching unit includes at least a differential connection state of detection sensors for obtaining a differential signal of detection signals of the respective detection sensors disposed at positions facing each other via the conveyance path, and the conveyance path. The addition connection state of the detection sensors for obtaining the addition signal of the detection signals of the respective detection sensors arranged at positions facing each other, and the detection of each detection sensor arranged apart from each other in the conveyance direction of the conveyance path The metal detection device according to claim 1, wherein the differential connection state of the detection sensor for obtaining a signal difference signal is switched. A magnetizer (4) for magnetizing a metal contained in a subject being transported by the transport mechanism;
The metal detection apparatus according to claim 1, wherein the detection sensor is a magnetic sensor that detects magnetized metal contained in a subject being transported. A common magnetic field generator (34) for forming an equal magnetic field at the position of each detection sensor in the plurality of detection sensors;
The metal detection apparatus according to claim 1, wherein the detection sensor detects a metal contained in a subject being transported based on a magnetic field formed by the common magnetic field generation apparatus.

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