JP2018141683A - Metal Detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detector with which it is possible to improve the accuracy of detecting metal in an inspection object.SOLUTION: The metal detector comprises: exciting coils 21a, 21b, wound in ring form inside a plane parallel to a conveyance plane on which an inspection object is carried in a prescribed direction of conveyance, for generating a magnetic field; and a detection coil 22, provided inside the exciting coil 21a, for detecting metal. The detection coil 22 includes a magnetic core of rectangular tabular shape arranged so that its longitudinal direction runs along the direction of conveyance and its plate thickness direction exists in a direction parallel to the surface of the exciting coil and orthogonal to the direction of conveyance, and at least a pair of coils wound around a magnetic core in mutually opposite directions and connected in series.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, a metal detector disclosed in Patent Document 1 is known as this type of metal detector.

  The conventional one described in Patent Document 1 includes an excitation coil 21 that is annularly wound in a plane parallel to a conveyance surface that conveys an object to be inspected in a predetermined conveyance direction, and generates a magnetic field. And a detection coil 22 for detecting metal. The detection coil 22 is arranged such that the longitudinal direction thereof is along the transport direction, a rectangular flat magnetic core 22a having a plate thickness direction in a direction substantially parallel to the surface of the excitation coil 21 and substantially perpendicular to the transport direction. And a pair of coils 22b and 22c that are wound around the magnetic core 22a in opposite directions and connected in series.

  With this configuration, the conventional one can further improve the detection sensitivity of the metal 6 based on the differential output voltage of the pair of coils 22b and 22c.

JP, 2006-217947, A

  However, in recent years, the market demand for higher detection sensitivity has been increasing, and further improvement in detection sensitivity has been desired.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a metal detector capable of improving the detection sensitivity of a metal in an object to be inspected.

  A metal detector according to claim 1 of the present invention is a metal detector for detecting the presence or absence of a metal (6) in an object to be inspected (5) moving in a magnetic field, wherein the object to be inspected moves. First and second exciting coils (21a and 21b) that are respectively annularly wound in two planes facing each other and generate the magnetic field, and the inside of the first or second exciting coil, or the A detection coil (22) provided between the first excitation coil and the second excitation coil for detecting the metal, the longitudinal direction of the detection coil being along the moving direction of the inspection object A rectangular flat plate-shaped magnetic core (22a, 23a, 24a) having a plate thickness direction in a direction parallel to the surfaces of the first and second exciting coils and perpendicular to the moving direction. , Wound around the magnetic core in opposite directions Re has at least a pair of coils connected in series (22b and 22c, 62a and 62b, 63a and 63 b) and a configuration with a.

  With this configuration, the metal detector according to claim 1 of the present invention includes the first and second exciting coils facing each other, the inside of the first or second exciting coil, or the first exciting coil and the second exciting coil. Since the detection coil provided between the two excitation coils is provided, the sensitivity region in which metal can be detected can be expanded as compared with the conventional one in which the detection coil is provided inside one excitation coil. Therefore, it is possible to improve the detection sensitivity of the metal in the inspection object.

  In the metal detector according to claim 2 of the present invention, the detection coil is wound around the magnetic core in the same direction instead of at least a pair of coils wound around the magnetic core in opposite directions and connected in series. And at least a pair of coils (26b, 26c).

  With this configuration, the metal detector according to claim 2 of the present invention includes an exciting coil wound in an annular shape in one of two planes facing each other, and in the other of the two planes. Since the detection region provided with the detection coil is provided with a detection coil provided on the inside of one excitation coil, the sensitivity region in which the metal can be detected can be expanded compared to the conventional one, so that in the inspection object. The detection sensitivity of the metal can be improved.

  According to a third aspect of the present invention, the metal detector further comprises phase adjusting means for making the phases of the currents flowing through the first and second exciting coils the same.

  With this configuration, the metal detector according to claim 3 of the present invention generates the first and second exciting coils by setting the phases of the currents flowing through the first and second exciting coils to the same phase. Therefore, the detection sensitivity of the metal in the inspection object can be improved.

  According to a fourth aspect of the present invention, there is provided a metal detector, comprising: a current supply unit that supplies a current of a predetermined frequency that generates the magnetic field to the first and second excitation coils; and a frequency setting that sets a frequency of the current. And means.

  With this configuration, the metal detector according to claim 4 of the present invention can easily detect the metal with the frequency of the magnetic field of the first and second exciting coils based on the assumed type of metal in the inspection object. Since the frequency can be set, the detection sensitivity of the metal in the inspection object can be improved.

  The metal detector according to a fifth aspect of the present invention further comprises transport means (41) having a transport surface (41a) for transporting the object to be inspected in the moving direction, and the first and second exciting coils. Has a configuration in which each is wound in an annular shape in two planes facing each other parallel or perpendicular to the transport surface.

  With this configuration, in the metal detector according to claim 5 of the present invention, the first and second exciting coils are respectively wound in an annular shape in two planes facing each other parallel or perpendicular to the transport surface. Even in this case, it is possible to improve the detection sensitivity of the metal in the inspection object.

  A metal detector according to a sixth aspect of the present invention has a configuration in which the coil intervals of the pair of coils (62a and 62b, 63a and 63b) are different from each other.

  With this configuration, the metal detector according to claim 6 of the present invention can have sensitivity in a wider sensitivity region by the detection coil having coils with different coil intervals.

  The present invention can provide a metal detector having an effect that the detection sensitivity of a metal in an object to be inspected can be improved.

It is a figure which shows typically the structure in 1st Embodiment of the metal detector which concerns on this invention. It is a figure which shows typically the metal detection processing apparatus in 1st Embodiment of the metal detector which concerns on this invention. It is a figure which shows typically the structure of the detection coil in 1st Embodiment of the metal detector which concerns on this invention. It is explanatory drawing of the principle of the metal detection in 1st Embodiment of the metal detector which concerns on this invention. It is a figure which shows an example of the arrangement | sequence of the magnetic core in 1st Embodiment of the metal detector which concerns on this invention. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the metal detection processing apparatus in the modification 1. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the arrangement | positioning of the excitation coil and detection coil in the modification 2. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the arrangement | positioning of the excitation coil and detection coil in the modification 2. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the arrangement | positioning of the excitation coil and detection coil in the modification 2. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the conveyance means in the modification 3. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is a figure which shows typically the conveyance means in the modification 3. FIG. In 1st Embodiment of the metal detector which concerns on this invention, it is sectional drawing which shows typically the structure of the detection coil in the modification 4. FIG. It is a figure which shows typically the structure in 2nd Embodiment of the metal detector which concerns on this invention.

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

(First embodiment)
First, the structure in 1st Embodiment of the metal detector which concerns on this invention is demonstrated using FIGS. 1-3.

  As shown in FIG. 1, the metal detector 1 in the present embodiment includes a metal detection processing device 10 that performs detection processing of metal that is a foreign object, and a conveyor 40 as a transport unit, The presence or absence of the metal 6 is detected.

  The metal detection processing apparatus 10 includes a metal detection unit 20 and a metal detection circuit 30. The conveyer 40 includes an endless annular conveyer belt 41 as conveying means for conveying the inspection object 5 in the illustrated conveying direction, and conveying rollers 42 and 43. The conveyor belt 41 has a transport surface 41a on which the inspection object 5 is placed and transported in the transport direction.

  As shown in FIG. 2, the metal detection circuit 30 includes an oscillator 31, amplifiers 32 (32 a to 32 d) as amplification means, a detection unit 33 (33 a to 33 d), and an ADC (analog / digital converter) 34 (34 a to 34 d). , A determination unit 35 (35a to 35d) as a determination unit, a result display unit 36, a frequency setting unit 37, and a phase adjustment unit 38 are provided.

  The metal detection unit 20 includes excitation coils 21 a and 21 b that generate a magnetic field, and a detection coil 22 that detects the metal 6 in the inspection object 5. The detection coil 22 is in a direction substantially parallel to the formation surface of the excitation coil 21a within the formation surface on which the excitation coil 21a is formed, and a direction substantially perpendicular to the conveyance direction (in the case of “width direction of the conveyance surface 41a”). Are arranged in 4 rows. In the present embodiment, an example in which the detection coils 22 are arranged in four rows is given, but the present invention is not limited to this, and may be one row, for example. In the drawing, the width direction of the transport surface 41 a is simply indicated as “width direction”.

  The exciting coils 21a and 21b have a rectangular shape. The exciting coil 21a is wound in an annular shape in a plane substantially parallel to the transport surface 41a in the vicinity of the transport surface 41a (see FIG. 1). The excitation coil 21b is separated from the excitation coil 21a by a predetermined distance, and is wound in a ring shape in a plane facing the excitation coil 21a. Each forming surface on which the exciting coils 21a and 21b facing each other sandwich a transport surface 41a on which the inspection object 5 is transported and moved. That is, the exciting coils 21a and 21b are respectively wound in an annular shape in two planes facing each other across the region in which the inspection object 5 moves. The exciting coils 21a and 21b are examples of first and second exciting coils, respectively.

  The number of turns of each of the exciting coils 21a and 21b is, for example, about 1 to 5 turns. The exciting coils 21a and 21b are connected to an oscillator 31 and generate a magnetic field in a region through which the inspection object 5 passes. In addition, the shape of the exciting coils 21a and 21b is not limited to a rectangular shape, and may be a circular shape, an elliptical shape, or the like.

  As shown in FIG. 3, the detection coil 22 includes a plurality of elongated rectangular flat magnetic cores 22a and a pair of coils 22b and 22c wound around the magnetic core 22a.

  The magnetic core 22a is formed of a flat-shaped magnetic body, for example, an amorphous magnetic body, and is arranged so that the longitudinal direction is along the transport direction. The magnetic core 22a has a plate thickness direction in the width direction of the transport surface 41a, and a plurality of magnetic cores 22a are stacked in the plate thickness direction. The magnetic core 22a may have a single configuration.

  Each of the coils 22b and 22c is wound around the stacked magnetic cores 22a in opposite directions and connected in series, and has a configuration of a pair of anti-series connection coils. One end of the coil 22b is connected to the input terminal of the amplifier 32 (see FIG. 2). The other end of the coil 22b is connected to one end of the coil 22c. The other end of the coil 22c is connected to the ground.

  Returning to FIG. 2, the oscillator 31 generates a current having a frequency of several kHz to 10 MHz, for example, and supplies the current to the excitation coils 21 a and 21 b of the metal detection unit 20 and the detection unit 33. The oscillator 31 is an example of a current supply unit.

  The amplifier 32 includes amplifiers 32a to 32d, each having one input terminal and one output terminal.

  Each of the amplifiers 32a to 32d has an input terminal connected to one end of the coil 22b, and amplifies the signal voltage difference from the two coils 22b and 22c forming a pair.

  The detection unit 33 includes detection units 33a to 33d. The detectors 33a to 33d are connected to the oscillator 31 and the output terminals of the amplifiers 32a to 32d, respectively, and synchronously detect the output signals of the amplifiers 32a to 32d in synchronization with the output of the oscillator 31. .

  The ADC 34 includes ADCs 34a to 34d. The ADCs 34a to 34d convert the output signals of the detectors 33a to 33d from analog signals to digital signals, respectively.

  The determination unit 35 includes determination units 35a to 35d. The determination units 35a to 35d are connected to the output terminals of the ADCs 34a to 34d, respectively, and based on these output signals, determine the presence or absence of the metal 6 in the inspection object 5 with reference to a predetermined determination threshold value. It is supposed to be.

  The result display unit 36 displays the determination result of the presence or absence of the metal 6 by the determination units 35a to 35d, for example, on a liquid crystal screen.

  The frequency setting unit 37 can set the oscillation frequency of the oscillator 31 based on the assumed type of the metal 6 in the inspection object 5. The frequency setting unit 37 is an example of a frequency setting unit.

  Specifically, when the metal 6 in the inspected object 5 is a magnetic metal (for example, iron), the frequency setting unit 37 sets the frequency of the oscillator 31 to a predetermined low frequency. On the other hand, when the assumed metal 6 in the inspected object 5 is a non-magnetic metal (for example, SUS304), the frequency setting unit 37 sets the frequency of the oscillator 31 to a predetermined high frequency. It should be noted that the relationship between the type of the metal 6 in the inspected object 5 and the frequency at which they are easy to detect is determined in advance by experiment, for example, five frequencies are determined, and the frequency is appropriately determined based on the type of the metal 6. If the frequency is changed, the detection sensitivity and workability can be improved.

  The phase adjustment unit 38 can eliminate a phase difference caused by a path difference or a circuit difference from the oscillator 31 to the excitation coils 21a and 21b by adjusting the phases of the currents flowing through the excitation coils 21a and 21b to the same phase. It is like that. Specifically, for example, the phase adjustment unit 38 obtains the phase difference between the currents flowing through the exciting coils 21a and 21b, and delays the phase of one of the currents that is advanced to match the phase of the other current. It has become. With this configuration, the metal detector 1 has a stronger magnetic field generated by the exciting coils 21 a and 21 b, and therefore it becomes easier to detect the metal 6 in the inspection object 5.

  Next, the principle of metal detection of the metal detection unit 20 will be described with reference to FIG. FIG. 4A is a plan view of the metal detection unit 20, and is a view of the detection coil 22 as viewed from above the excitation coil 21b. FIG. 4B is a cross-sectional view in the transport direction in FIG. FIG. 4C is a cross-sectional view in the transport direction when the inspection object 5 includes the metal 6. For the sake of simplicity, it is assumed that there is one detection coil 22 having one magnetic core 22a inside the excitation coil 21a.

  As shown in FIGS. 4A and 4B, in the detection coil 22, the longitudinal direction of the magnetic core 22a having a plate thickness direction in the width direction of the transport surface 41a is along the transport direction inside the excitation coil 21a. Has been placed. The coils 22b and 22c are wound in opposite directions and connected in series.

  That is, the direction of the magnetic field generated by the excitation coils 21a and 21b and the sensitivity axis of the detection coil 22 are orthogonal. The arrangement position of the detection coil 22 is adjusted so that no induced voltage is generated even if an alternating current is passed through the excitation coils 21a and 21b. Normally, if the detection coil 22 is arranged at the center between the left coil 21a1 and the right coil 21a2 of the excitation coil 21a, no induced voltage is generated. Here, that the induced voltage does not occur does not only mean that the induced voltage is zero volts, but means that the induced voltage is low enough to detect the metal 6.

  Further, in addition to the above arrangement, the metal detector 1 has a detection coil 22 connected in a differential configuration, so that high balance can be realized and highly sensitive detection is possible.

  Furthermore, since the metal detector 1 uses the thickness direction of the magnetic core 22a as the width direction of the transport surface 41a, the cross-sectional area through which the magnetic flux generated by the excitation coils 21a and 21b can pass is extremely narrow, and the magnetic core 22a. In this structure, eddy currents are difficult to generate. As a result, compared to the case where the plate thickness direction of the magnetic core 22a is orthogonal to the transport surface 41a, the metal detector 1 is (1) the power of the exciting coils 21a and 21b is not easily consumed by eddy currents. (2) Since eddy currents are less likely to occur in the magnetic core 22a, the output signals of the detection coils 22 can be easily balanced, and the output signals can be stabilized.

  Furthermore, since the metal detector 1 can increase the volume of the magnetic material by laminating the magnetic cores 22a in the plate thickness direction, the metal detection sensitivity can be further improved.

  The coil wire used between the coil 22b and the coil 22c or at the connection portion from the detection coil 22 to the outside is preferably a twisted pair wire in order to avoid the influence of the magnetic field.

  As shown in FIG. 4C, when the metal 6 passes through the upper part of the metal detection unit 20, a new magnetic field is generated in the metal 6 by the magnetic field generated by the excitation coils 21a and 21b. In this case, the mechanism differs depending on whether the metal 6 is a conductor or a magnetic material. In the case of a magnetic material, the metal 6 is magnetized to generate a new magnetic field, and in the case of a conductor, an eddy current is generated in the metal 6 to generate a new magnetic field. When the metal 6 passes near the center of the coils 22b and 22c, in the state shown in FIG. 4C, the newly generated magnetic field is in the direction opposite to the conveying direction in the coil 22b and in the conveying direction in the coil 22c. Flowing into. As a result, an induced voltage generated by a new magnetic field is generated in the detection coil 22, and the induced voltage of the detection coil 22 is added by the amplifier 32 and synchronously detected by the detection unit 33, whereby a spike-like voltage signal (FIG. 2) is obtained. Reference) will occur.

  Next, a modification of the detection coil 22 will be described with reference to FIG. In the above description, the detection coil 22 has a configuration in which the coils 22b and 22c are wound around one magnetic core 22a. This invention is not limited to this, It can also be set as the structure which has arrange | positioned the several magnetic core side by side in the conveyance direction. Hereinafter, an example in which two magnetic cores are arranged in the transport direction will be described.

  FIG. 5A shows an example in which the detection coils 23 and 24 are arranged in a line substantially along the transport direction. The detection coils 23 and 24 have magnetic cores 23a and 24a, respectively. The magnetic cores 23a and 24a have coils 23b and 24b wound individually. The coils 23b and 24b are wound in opposite directions and connected in series. FIG. 5B shows a configuration in which the detection coils 23 and 24 are arranged substantially along the conveyance direction, and the detection coil 24 is arranged inclined at a predetermined angle with respect to the conveyance direction. FIG. 5C shows a configuration in which the detection coils 23 and 24 are both arranged in a line inclined at substantially the same angle with respect to the transport direction. FIG. 5D shows a configuration in which the detection coils 23 and 24 are arranged at different angles with respect to the transport direction.

  The metal 6 (see FIG. 1) is actually assumed to have various shapes (for example, a needle shape). When the metal 6 is not a perfect sphere, directivity is generated in the magnetic field generated by the magnetized metal 6. In that case, by configuring the detection coil as shown in FIG. 5, the metal detector 1 in the present embodiment can improve the detection sensitivity.

  Next, operation | movement of the metal detector 1 in this embodiment is demonstrated using FIG.1 and FIG.2.

  The oscillator 31 generates a current having a frequency set by the frequency setting unit 37, for example, a frequency of 100 kHz, and supplies the current to the excitation coils 21 a and 21 b of the metal detection unit 20 and the detection unit 33. As a result, the exciting coils 21a and 21b generate a magnetic field in a region through which the inspection object 5 passes.

  The phase adjustment unit 38 adjusts the phases of the currents flowing through the excitation coils 21a and 21b to the same phase.

  When the inspection object 5 including the metal 6 passes near the upper part of the detection coil 22 in a state where the excitation coils 21 a and 21 b generate a magnetic field, a new magnetic field is generated by the metal 6. An induced voltage generated by the new magnetic field is generated in the detection coil 22.

  The amplifier 32 adds and amplifies each induced voltage generated by the two coils 22 b and 22 c forming a pair, and outputs the amplified voltage to the detector 33.

  The detection unit 33 outputs a spike-shaped voltage signal to the ADC 34 by synchronously detecting the signal amplified by the amplifier 32 based on the transmission signal from the oscillator 31.

  The ADC 34 converts the voltage signal from the detection unit 33 from an analog value to a digital value signal and outputs the signal to the determination unit 35.

  The determination unit 35 determines the presence / absence of the metal 6 in the inspection object 5 based on the output signal of the ADC 34 and a predetermined threshold for determination, and outputs data of the determination result to the result display unit 36.

  The result display unit 36 displays the determination result by the determination unit 35 on, for example, a liquid crystal screen. Here, the result display unit 36 has a configuration for displaying the determination result for each detection coil 22, and preferably displays the position where the metal 6 in the inspection object 5 is detected.

  Next, a modified example of the metal detector 1 in the present embodiment will be described. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned metal detector 1, and the description is abbreviate | omitted.

[Modification 1]
FIG. 6 shows a metal detection processing apparatus according to the first modification. The metal detection unit 20 of this metal detection processing apparatus includes one detection coil 25. In the detection coil 25, a plurality of cores 22a are stacked to the same extent as the length in the width direction of the transport surface 41a (see FIG. 1). Coils 22b and 22c are wound in opposite directions and connected in series to the laminated magnetic core 22a. One amplifier 32 is connected to the coils 22b and 22c. With this configuration, the metal detection processing device according to the first modification can be configured with one each from the amplifier 32 to the determination unit 35, and thus the circuit configuration can be simplified.

[Modification 2]
Next, Modification 2 will be described with reference to FIGS. This modification 2 relates to the arrangement of the excitation coils 21a and 21b and the detection coil 22 in the present embodiment. In addition, the side where the above-mentioned conveyance surface 41a exists is called the upper side belt 41b, and the belt under it is called the lower side belt 41c.

  In FIG. 7, the exciting coils 21a and 21b are respectively wound annularly in two opposing planes parallel to the transport surface 41a, the exciting coil 21b is located above the upper belt 41b, and the detection coil 22 is located above. The example of a structure arrange | positioned below the belt 41b is shown typically.

  In the configuration example shown in FIGS. 7A and 7B, the detection coil 22 is disposed in the vicinity of the lower surface of the upper belt 41b (the surface opposite to the conveying surface 41a).

  As shown in FIG. 7A, the excitation coil 21a and the detection coil 22 are between the upper belt 41b and the lower belt 41c, the detection coil 22 is on the upper belt 41b side, and the excitation coil 21a is on the lower belt 41c side. In addition, it may be configured to be provided respectively.

  Further, as shown in FIG. 7B, the detection coil 22 may be disposed between the upper belt 41b and the lower belt 41c, and the excitation coil 21a may be disposed near the lower surface of the lower belt 41c. .

  In the configuration example shown in FIGS. 7C and 7D, the detection coil 22 is disposed in the vicinity of the lower surface of the lower belt 41c.

  As shown in FIG. 7C, the excitation coil 21a and the detection coil 22 are provided below the lower belt 41c, and the detection coil 22 is provided inside the excitation coil 21a (similar to FIG. 2). You can also.

  Further, as shown in FIG. 7D, the excitation coil 21a and the detection coil 22 may be provided below the lower belt 41c, and the excitation coil 21a may be provided below the detection coil 22.

  In FIG. 8, the exciting coils 21a and 21b are respectively wound annularly in two opposed planes parallel to the conveying surface 41a across the conveying surface 41a, and the exciting coil 21b and the detection coil 22 are connected to the upper belt 41b. A configuration example in which the excitation coil 21a is disposed below the upper belt 41b is shown schematically above.

  In the configuration example shown in FIGS. 8E and 8F, the detection coil 22 is provided inside the excitation coil 21b (similar to FIG. 2).

  As shown in FIG. 8E, the detection coil 22 may be provided inside the excitation coil 21b, and the excitation coil 21a may be disposed near the lower surface of the upper belt 41b.

  As shown in FIG. 8 (f), the detection coil 22 may be provided inside the excitation coil 21b, and the excitation coil 21a may be disposed near the lower surface of the lower belt 41c.

  In the configuration example shown in FIGS. 8G and 8H, the excitation coil 21b and the detection coil 22 are arranged on the upper side of the upper belt 41b, and the detection coil 22 is provided on the lower side of the excitation coil 21b. In this case, the inspection object 5 passes between the detection coil 22 and the upper belt 41b.

  As shown in FIG. 8G, the excitation coil 21b and the detection coil 22 are located above the upper belt 41b, the detection coil 22 is provided between the excitation coil 21b and the upper belt 41b, and the excitation coil 21a is connected to the upper belt 41b. It can also be set as the structure arrange | positioned in the vicinity of the lower surface of 41b.

  Further, as shown in FIG. 8 (h), the excitation coil 21b and the detection coil 22 are on the upper side of the upper belt 41b, the detection coil 22 is provided between the excitation coil 21b and the upper belt 41b, and the excitation coil 21a is provided. It can also be set as the structure arrange | positioned in the vicinity of the lower surface of the lower side belt 41c.

  In FIG. 9, the exciting coils 21a and 21b are respectively wound in an annular shape in two opposing planes perpendicular to the conveying surface 41a, and the exciting coil 21a and the detecting coil 22 are arranged in the conveyor belt 41 in the conveying direction. A configuration example in which the exciting coil 21b is arranged on the left side of the conveyor belt 41 is schematically shown on the right side of FIG.

  As shown to Fig.9 (a), it can also be set as the structure which provides the detection coil 22 inside the excitation coil 21a (similar to FIG. 2) in the right side of the conveyor belt 41 toward the conveyance direction.

  Further, as shown in FIG. 9B, the detection coil 22 may be arranged between the excitation coil 21 a and the conveyor belt 41 on the right side of the conveyor belt 41 in the transport direction.

  9A and 9B, the detection coil 22 may be arranged on the left side of the conveyor belt 41 in the transport direction.

[Modification 3]
Next, Modification 3 will be described with reference to FIGS. 10 and 11. This modified example 3 replaces the conveyor 40 as the conveying means in the present embodiment.

  FIG. 10 shows a main part of a metal detector equipped with a slide-like transport unit 45 as a transport means. The transport unit 45 is formed of a non-metallic material, for example, a resin. The inspection object 5 slides down the transport unit 45 while being accelerated by gravity.

  As shown in FIG. 10, for example, the excitation coil 21 a and the detection coil 22 are arranged on the conveyance unit 45 side and the excitation coil 21 b is arranged on the opposite side of the conveyance unit 45. Even so, the metal 6 in the inspection object 5 can be detected as in the embodiment shown in FIG.

  FIG. 11 shows a main part of a metal detector provided with, for example, a cylindrical passage 46 as a conveying means. The passage part 46 is made of a non-metallic material, for example, a resin. The inspection object 5 naturally falls inside the passage portion 46 while being accelerated by gravity.

  As shown in FIG. 11, even if the inspection object 5 is naturally dropped by disposing the exciting coil 21a, the detection coil 22 and the exciting coil 21b so as to sandwich the passage portion 46, FIG. The metal 6 in the inspection object 5 can be detected similarly to the embodiment shown in FIG.

[Modification 4]
In the above-described embodiment, the coils 22b and 22c wound in opposite directions and connected in series have been described as an example (see FIGS. 2 and 3). FIG. 12 shows a configuration of Modification 4 instead of this.

  As shown in FIG. 12, the detection coil 26 according to the fourth modification includes a plurality of elongated rectangular flat magnetic cores 26a and a pair of coils 26b and 26c wound around the magnetic core 26a.

  The coils 26b and 26c are wound around the laminated magnetic core 26a in the same direction. One end of the coil 26 b is connected to one input terminal of the differential amplifier 38. The other end of the coil 26b is connected to the ground. One end of the coil 26 c is connected to the other input terminal of the differential amplifier 38. The other end of the coil 26c is connected to the ground.

  The output terminal of the differential amplifier 38 is connected to the detection unit 33. The configuration after the detection unit 33 is the same as the configuration shown in FIGS.

  With the above-described configuration, the detection coil 26 according to Modification 4 has the same function as the coils 22b and 22c wound in opposite directions and connected in series.

  As described above, the metal detector 1 in the present embodiment is provided between the exciting coils 21a and 21b facing each other and the inside of the exciting coil 21a or the exciting coil 21b, or between the exciting coil 21a and the exciting coil 21b. Since the detection coil 22 is provided, the sensitivity region in which the metal can be detected can be expanded as compared with the conventional one in which the detection coil is provided inside one excitation coil. The detection sensitivity can be improved.

(Second Embodiment)
The structure of the metal detector in this embodiment is demonstrated using FIG.

  As shown in FIG. 12, the metal detector in this embodiment is different in that a metal detection processing device 50 is provided instead of the metal detection processing device 10 (see FIG. 2) in the first embodiment. Therefore, the description of the same structure as the first embodiment is omitted.

  The metal detection processing device 50 includes a metal detection unit 60 and a metal detection circuit 70. The metal detection unit 60 includes excitation coils 21 a and 21 b and a detection coil 61. The metal detection circuit 70 includes an oscillator 31, an amplifier 32 (32a to 32b) as an amplification unit, a detection unit 33 (33a to 33b), an ADC 34 (34a to 34b), a determination unit 35 (35a to 35b) as a determination unit, A result display unit 36 is provided.

  The detection coil 61 is arranged in a direction substantially coinciding with the transport direction. In the present embodiment, an example is described in which one detection coil 61 is arranged in a direction substantially orthogonal to the conveyance direction. However, the present invention is not limited to this, and a plurality of detection coils may be arranged. .

  The detection coil 61 includes a core 22a laminated in the same manner as in the first modification of the first embodiment (see FIG. 6), two pairs of coils 62a and 62b wound around the laminated magnetic core 22a, and coils 63a and 63b. And having.

  In the coils 62a and 62b, which are a pair of coils, one end of the coil 62a is connected to the input terminal of the amplifier 32b, the other end of the coil 62a is connected to one end of the coil 62b, and the other end of the coil 62b is connected to the ground. Has been.

  In the coils 63a and 63b, which are the other pair of coils, one end of the coil 63a is connected to the input terminal of the amplifier 32a, the other end of the coil 63a is connected to one end of the coil 63b, and the other end of the coil 63b is connected to the ground. Has been.

  In the present embodiment, the detection coil 61 has two pairs of coils 62a and 62b and coils 63a and 63b, the coil interval between one pair of coils 62a and 62b, and the coil between the other pair of coils 63a and 63b. The intervals are different from each other. That is, the coil interval between one pair of coils 62a and 62b is wider than the coil interval between the other pair of coils 63a and 63b.

  With this configuration, the metal detection processing device 50 according to the present embodiment has sensitivity in a wider sensitivity region by the two pairs of coils 62a and 62b and coils 63a and 63b having different coil intervals. Specifically, the metal detection processing device 50 has a metal detection sensitivity at a relatively distant position by one pair of coils 62a and 62b, and a metal detection sensitivity at a relatively close position by the other pair of coils 63a and 63b. Have

  Therefore, in addition to the effects of the first embodiment, the metal detector in the present embodiment can improve the detection sensitivity of the metal 6 in the inspection object 5 and save space, and can reduce the cost. Furthermore, it has sensitivity in a wider sensitivity range.

  In the second embodiment, two pairs of coils have been described as examples. However, the present invention is not limited to this, and a configuration in which three or more pairs of coils are provided in the magnetic core 22a is also possible. Good. The metal detector having this configuration has a sensitivity in a wider sensitivity region than that using two pairs of coils.

  Further, the two pairs of coils described in the second embodiment are replaced with two pairs of coils wound in the same direction as described in the fourth modification of the first embodiment, and the outputs of these coils are differentially set. The same effect can be obtained by a configuration in which amplification is performed by an amplifier.

  As described above, the metal detector according to the present invention has an effect that the detection sensitivity of the metal in the inspection object can be improved, and the presence / absence of the metal in the inspection object such as food or medicine is detected. It is useful as a metal detector to detect.

DESCRIPTION OF SYMBOLS 1 Metal detector 5 Inspected object 6 Metal 10, 50 Metal detection processing apparatus 20, 60 Metal detection part 21a Excitation coil (1st excitation coil)
21b Excitation coil (second excitation coil)
22, 23, 24, 25, 61 Detection coil 22a, 23a, 24a Magnetic core 22b, 22c, 23b, 24b, 62a, 62b, 63a, 63b Coil 30, 70 Metal detection circuit 31 Oscillator (current supply means)
32 (32a to 32d) amplifier (amplifying means)
35 (35a-35d) determination part (determination means)
37 Frequency setting part (frequency setting means)
38 Differential amplifier 41 Conveyor belt (conveying means)
41a Conveying surface 45 Conveying section (conveying means)
46 Passing part (conveying means)

Claims (6)

A metal detector for detecting the presence or absence of a metal (6) in an inspection object (5) moving in a magnetic field,
First and second exciting coils (21a and 21b) that are respectively annularly wound in two planes facing each other across an area in which the inspection object moves, and generate the magnetic field;
A detection coil (22) for detecting the metal provided inside the first or second excitation coil or between the first excitation coil and the second excitation coil;
With
The detection coil is
A rectangular plate having a plate thickness direction in a direction parallel to the surfaces of the first and second exciting coils and perpendicular to the moving direction, the longitudinal direction being arranged along the moving direction of the inspection object Magnetic cores (22a, 23a, 24a),
At least a pair of coils (22b and 22c, 62a and 62b, 63a and 63b) wound in opposite directions around the magnetic core and connected in series;
A metal detector characterized by comprising:   The detection coil includes at least a pair of coils (26b, 26c) wound around the magnetic core in the same direction instead of at least a pair of coils wound around the magnetic core in opposite directions and connected in series. The metal detector according to claim 1.   3. The metal detector according to claim 1, further comprising a phase adjusting unit configured to set phases of currents flowing through the first and second exciting coils to the same phase. 4. Current supply means for supplying a current of a predetermined frequency for generating the magnetic field in the first and second exciting coils;
Frequency setting means for setting the frequency of the current;
The metal detector according to any one of claims 1 to 3, further comprising: A transport means (41) having a transport surface (41a) for transporting the inspection object in the moving direction;
The first and second exciting coils are each wound in an annular shape in two planes facing each other parallel or perpendicular to the transport surface. 5. The metal detector according to any one of up to 4.   The metal detector according to any one of claims 1 to 5, wherein a coil interval of each of the pair of coils (62a and 62b, 63a and 63b) is different from each other.

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