JPH08101279A - Metal detector - Google Patents

Abstract

PURPOSE: To obtain a highly sensitive metal detector by utilizing the high sensitivity regions of transmission coil and receiving coil. CONSTITUTION: A metal 8 mixed into an object 7 carried on a carrying means 1 is magnetized by the field generated from a transmission coil 4 or an eddy current is induced. The difference between outputs from receiving coils 5 and 6 is determined and the electromotive force, induced by the field of the transmission coil 4, is offset thus detecting the metal 8. Since the metal 8 passes through the transmission coil 4 and the receiving coil 5 arranged in a substantially identical plane, high detection sensitivity is ensured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detector for detecting metal pieces mixed in products such as foods, medicines, clothes and other products related to daily life and raw materials for processing, and particularly to a transmitting / receiving coil. The present invention relates to a metal detector in which the detection sensitivity is improved by making use of a region having good detection sensitivity.

[0002]

2. Description of the Related Art When manufacturing products such as foods, medicines, and clothes, metal may be mixed into the products due to a part of the manufacturing apparatus being cut off or a sewing machine needle for sewing being broken. To maintain product safety, it is necessary to remove metal or eliminate products containing metal. A device called a metal detector is usually used to detect the metal mixed in the product. A metal detector applies a magnetic field to a product to be measured, and utilizes the fact that the magnetic field changes due to the presence of metal. As a method of applying a magnetic field, a method of passing a current through a coil to generate a magnetic field is used, and as a method of detecting a change in a magnetic field, a method of detecting a voltage change induced in the coil is used. Usually, a coil that generates a magnetic field is called a transmission coil, a coil that detects a change in a magnetic field is called a reception coil, and the transmission coil and the reception coil are collectively called a detection head.

In this type of metal detector, various detection head shapes have been proposed in order to improve the detection sensitivity.
As a typical conventional shape, as shown in Japanese Patent Application No. 58-34397, one transmitting coil 4 and two receiving coils 5 and 6 are provided so as to face each other, and the DUT 7 is set to the transmitting coil 4 and the receiving coil. What is called an opposed type that passes between 5 and 6 (the basic structure is shown in FIG. 10), and Japanese Utility Model Application No. 53-1
No. 77263, the transmission coil 4 is sandwiched between the two reception coils 5 and 6, and the transmission coil 4 and the reception coils 5 and 6 are arranged so as to be perpendicular to the belt 1 which is the conveying means. , What is called a coaxial type in which the DUT 7 is arranged so as to pass through these three transmitting and receiving coils (the basic configuration is shown in FIG. 11), and Japanese Patent Application No.
No. 237615, the transmission coil 4 is arranged so as to be parallel to the traveling direction of the belt in the vicinity of the belt 1 which is the transporting means, and the transmitting coil 4 is disposed substantially in the same plane as the traveling direction of the belt. The two receiving coils 5 and 6 are arranged at the front and rear positions so that the DUT 7 passes near these three coils, which is called a horizontal one-sided shape (Fig. 12).
The basic configuration is shown).

[0004]

The conventional metal detector having the above-described structure cancels the magnetic field generated by the transmitting coil and detects only the magnetic field generated by the metal. On the other hand, because the two receiving coils are placed in front of and behind the traveling direction of the object to be measured so as not to be affected by the metal as much as possible, the ability of the receiving coil to magnetize the metal held or the eddy current in the metal. It is impossible to detect minute metal because the metal detector has a limit in its detection sensitivity because it does not fully utilize the area with a large ability to generate Met.

An object of the present invention is to solve the problems of the conventional metal detector, such as not using the regions with good detection ability of the transmitter coil and the receiver coil, and to provide a metal detector with high detection sensitivity. is there.

[0006]

In order to solve the above-mentioned problems, a metal detector of the present invention is a metal detector which conveys an object to be inspected for metal contamination, and a surface which interrupts the conveyance path of the conveyer. And a transmitter coil having an opening through which the DUT passes therethrough, which generates a magnetic field by passing an electric current, and which is substantially in the same plane as the plane, One of them comprises at least two receiving coils having an opening through which the DUT passes.

[0007]

In the above-mentioned "at least two receiving coils", one of them is a receiving coil having an opening through which the object to be measured passes, and if there are a plurality of other receiving coils, the total thereof is obtained. Is used to cancel the output due to the magnetic field of the transmitter coil. Here, in order to avoid the complexity of the description, it is assumed that the number of the other receiving coils is one. When the DUT is not mixed, the output voltages of the detection signals of the two receiving coils are adjusted to be almost equal. Therefore, when the detection signals of the two receiving coils are input to the differential amplifier, the output voltage of the differential amplifier is zero volt. When magnetic metal such as iron is mixed in the object to be measured, when the magnetic metal is magnetized by the magnetic field generated by the transmitting coil, a new magnetic field is generated, and the two receiving coils are separated from the magnetic field by the transmitting coil. A magnetic field obtained by combining the magnetic fields generated by the magnetization of the magnetic metal is detected. When the signals of the two receiving coils are input to the differential amplifier, the magnetic fields of the transmitting coils are canceled out, and only the magnetic field of the magnetic metal can be detected. The voltage output by the differential amplifier changes with the movement of the metal, and has a characteristic waveform having a frequency component proportional to the moving speed.

Further, when a non-magnetic metal such as SUS304 stainless steel or SUS316 stainless steel is mixed in the object to be measured, an eddy current flows in the mixed non-magnetic metal due to the magnetic field generated by the transmission coil, and a new magnetic field is generated. A magnetic field is generated. The two receiving coils detect the combined magnetic field of the magnetic field of the transmitting coil and the magnetic field of the eddy current. When the signals of the two receiving coils are input to the differential amplifier, the magnetic fields of the transmitting coils are canceled out, and only the magnetic field of the eddy current can be detected. The voltage output by the differential amplifier changes with the movement of the metal, and has a characteristic waveform having a frequency proportional to the moving speed.

In the metal detector based on the principle as described above, the closer the magnetic metal or the non-magnetic metal is to the transmitting coil that generates a magnetic field, the stronger the magnetic coil and the non-magnetic metal are, regardless of the orientation, spacing, and arrangement of the transmitting coil and the receiving coil. It can be magnetized and can flow strong eddy currents. Further, the magnetized or eddy current flowing metal can generate a larger electromotive force as it is closer to the receiving coil. In particular, the maximum electromotive force is obtained when the transmitter coil and the receiver coil are in the same plane and the metal is in the transmitter coil and the receiver coil on the same plane.

In the metal detector of the present invention, in order to make the difference between the outputs of the two receiving coils as large as possible, one receiving coil is arranged so as not to be influenced by the metal, that is, the two receiving coils are arranged. Without being bound by the conventional design method of arranging them in the front-back direction with respect to the traveling direction of the DUT, we conducted a numerical study based on the electromagnetic theory and constructed the transmitter coil and the receiver coil on almost the same plane, Has an optimum coil shape and configuration that allows one to pass through one of the receiving coils in this plane. Since it is configured in this way, it is suitable for the above-mentioned conditions for obtaining a large electromotive force,
Detects metal with high sensitivity.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the metal detector of the present invention will be described with reference to FIG. A belt 1, which is a conveying unit 1 that conveys an object to be measured, is driven by two rollers 2 and 3 and conveys an object to be measured 7 from left to right at a constant speed. The transmission coil 4 so as to surround the belt 1 (in other words, so that the DUT 7 passes through the opening 4a of the transmission coil 4).
Are arranged substantially perpendicular to the conveying direction of the belt 1. Two receiving coils 5 and 6 that generate a voltage by the magnetic field generated by the transmitting coil 4 are arranged on a surface substantially the same as the surface on which the transmitting coil 4 is arranged. One receiving coil 5 is arranged so as to surround the belt 1, and the other receiving coil 6 is arranged below the belt 1.

The AC signal generated by the reference signal generator 9 is applied to the transmission coil 4 via the filter 10 and the power amplifier 11. The transmission coil 4 generates an alternating magnetic field by this AC signal. The two receiving coils 5 and 6 arranged on substantially the same surface as the transmitting coil 4 receive the magnetic field generated by the transmitting coil 4 and respectively generate electromotive force. The electromotive force of the two receiving coils 5 and 6 is input to the differential amplifier 12. Normally, the voltage output from the differential amplifier 12 is adjusted to zero volt. Here, when the DUT 7 in which the metal 8 is mixed passes through the transmitting coil 4 and the receiving coil 5, a signal corresponding to the size of the metal 8 and its position is output from the differential amplifier 12. . The signal output from the differential amplifier 12 is input to the first detection circuit 14 and the second detection circuit 15. The signal input to the first detection circuit 14 is synchronously detected at the phase set in the phase shift circuit 13 (the same phase as the transmission coil), and the output signal is the bandpass filter 1
6, determination means 2 via amplifier 18, A / D converter 20
Entered in 2. This signal is used to detect magnetic metal such as iron. On the other hand, the signal input to the second detection circuit 15 has a phase set by the phase shift circuit 13 (first detection circuit 1
4 is 90 degrees delayed from the phase of the signal sent to 4), and the output signal is band-pass filter 17, amplifier 19,
It is input to the determination means 22 via the A / D converter 21.
This signal is used to detect a non-magnetic material such as SUS304 stainless steel. The determination means 22 determines the presence or absence of metal inclusion by comparing the maximum value of the input signal with the determination reference value, for example.

In the first embodiment, the belt 1 which is the conveying means passes through the inside of the receiving coil 5 at the upper portion, but can pass through the receiving coil 6 at the lower portion. The second embodiment thus configured is shown in FIG. The belt 1, which is a conveying unit, is driven by two rollers 2 and 3 and conveys the DUT 7 from left to right at a constant speed. A transmission coil 4 is arranged so as to surround the belt 1 so as to be substantially perpendicular to the conveyance direction of the belt 1. Two receiving coils 5 and 6 that generate a voltage by the magnetic field generated by the transmitting coil 4 are arranged on a surface substantially the same as the surface on which the transmitting coil 4 is arranged. One receiving coil 6 is arranged so as to surround the belt 1, and the other receiving coil 5 is arranged above the belt 1. Since the features of the present invention are the one-sided detection head and the configuration (positional relationship) between the detection head and the transport path, the description and illustration of the electrical signal system will be omitted in the second and subsequent embodiments.

As another embodiment of the metal detector of the present invention, one shown in FIGS. 3, 4 and 5 is also conceivable. The third embodiment shown in FIG. 3 is an embodiment in which the detection head is a detection head having a shape bent around an axis in a direction perpendicular to the conveyance surface of the belt 1 as a conveyance means. In the third embodiment, the belt 1, which is the conveying means, passes through the upper receiving coil 5, but as in the second embodiment, it passes through the lower receiving coil 6. You may allow it. The fourth embodiment shown in FIG. 4 is an embodiment in which a planar detection head is provided at an angle in the left-right direction with respect to the belt 1 which is the conveying means. In the fourth embodiment, the belt 1, which is the conveying means, passes through the lower receiving coil 6, but it may pass through the upper receiving coil 5. The fifth embodiment shown in FIG. 5 is an embodiment in which a flat type detection head is provided at an angle in the vertical direction with respect to the belt 1 which is the conveying means. In the fifth embodiment, the belt 1, which is the conveying means, passes through the upper receiving coil 5, but it may pass through the lower receiving coil 6. According to the third to fifth embodiments, the influence of the object to be measured itself can be reduced by, for example, the object to be measured having a rectangular parallelepiped obliquely entering the transmitting and receiving coil surface from the corner. The third embodiment and the fourth embodiment are effective for, for example, a rectangular parallelepiped object to be measured long in the transport direction, and the fifth embodiment is effective for a rectangular parallelepiped object to be measured long in the direction perpendicular to the transport direction. Is.

Next, a sixth embodiment intended to miniaturize the detection head in the metal detector of the present invention will be described with reference to FIG. The transmission coil 4 is provided so that the belt 1 passes through the opening 4a in a plane perpendicular to the conveying direction of the belt 1 which is the conveying means. The receiving coil 5 is provided in the same plane as the transmitting coil 4 so that the belt 1 passes through the opening 5a. On the other hand, the receiving coil 6 has a smaller area for receiving the magnetic flux than the receiving coil 5, and is provided in the lower part in the same plane as the receiving coil 5. In this case, although the electromotive forces of the receiving coil 5 and the receiving coil 6 are different, the number of turns of the coil and the area of the portion surrounded by the coil are adjusted so that the amount of magnetic flux multiplied by the number of turns becomes equal. Thus, the electromotive forces of the two receiving coils 5 and 6 can be equalized. When the number of turns and the area are not adjusted, the output voltage can be adjusted by adding an electric circuit such as an amplifier in the subsequent stage. With such a configuration, it becomes possible to configure a small detection head. In addition, as in the seventh embodiment shown in FIG. 7, the receiving coil 5 provided in the lower portion may be provided in the upper portion so that the object to be measured 7 is passed therethrough and the enclosed area is small.

Furthermore, FIG. 8 shows an eighth embodiment of the metal detector of the present invention. In the eighth embodiment, the receiving coil, through which the DUT 7 does not pass, is provided outside the transmitting coil 4 that generates a magnetic field as the second receiving coil 6a and the third receiving coil 6b on the left and right. It is located almost on the same plane as. The first receiving coil 5 through which the DUT 7 passes has a substantially same shape as the transmitting coil 4, and is arranged on the substantially same plane so as to overlap with the transmitting coil 4. In the present embodiment, since the receiving coil for canceling the voltage generated by the magnetic field generated by the transmitting coil 4 is provided separately on the left and right sides, the effect of the magnetic field of the metal 8 on the receiving coil in which the metal 8 does not pass through the receiving coil is separated. Can be made smaller. In the present embodiment, the second receiving coil 6a and the third receiving coil 6b are arranged on the left and right outside the same surface of the transmitting coil 4, but may be arranged above and below the same surface of the transmitting coil 4. Also,
In this example, the number is two, but the number of receiving coils through which the DUT 7 does not pass may be three or more.

As an implementation method of the detection head used in the present invention, an embodiment shown in FIG. 9 can be considered. The transmitting coil 4 and the receiving coils 5 and 6 are patterned on the insulating substrate 23 using a photoetching technique. Next, the DUT 7 passes through the opening 4a of the transmission coil 4 (also the opening 5a of the reception coil 5). By thus providing the transmitting and receiving coils 4 and 5 on the same substrate, it is possible to reduce fluctuations in the coil spacing, and it is possible to configure a stable detection head. The stability of the detection head means
It also improves the detection sensitivity.

In Table 1, the conditions such as the size of the opening through which the object to be measured passes are the same, and the respective sensitivities of the facing type, the coaxial type, the horizontal one-sided type, and the metal detector of the present invention are passed through the metal. An example of numerical calculation obtained from the relationship with the height z will be shown. The passing height z is the height from the receiving coil arranged below in the case of the opposed type, the height from the lower part of the coil in the case of the coaxial type, and from the surface on which the transmitting / receiving coil is arranged in the case of the horizontal one-sided type. In the case of the metal detector of the present invention is the height from the lower part of the receiving coil through which the belt as the conveying means passes.

[0019]

[Table 1]

From Table 1, it can be seen that the metal detector of the present invention has a metal passing height of 10 mm, which is about 1.3 times that of the horizontal single-faced type.
It is possible to obtain detection sensitivity about 8 times that of the coaxial type and about 86 times that of the opposed type. Further, it can be seen that even at a passing height of 60 mm, there is a detection sensitivity of about 4.7 times that of the horizontal flat surface type, about 2.1 times that of the coaxial type, and about 8.3 times that of the facing type.

Table 2 shows, in the metal detector of the present invention, when the detection head is tilted in the left-right direction with respect to the conveying direction of the belt 1 as the conveying means (see the fourth embodiment shown in FIG. 4,
However, when the belt 1 passes through the opening of the receiving coil 5 as in the first embodiment) and is tilted in the vertical direction with respect to the conveying direction of the belt 1 (see the fifth embodiment shown in FIG. 5), When the detection head of the metal detector of the invention is arranged perpendicularly to the conveyance direction of the belt 1 (see the first embodiment shown in FIG. 1) and the coaxial type (see FIG. 11), the detection sensitivity can be numerically calculated. The result of comparison is shown. The conditions such as the size of the opening through which the DUT 7 passes are the same. The transmission coil 4 and the reception coil 5 of the metal detector of the present invention are arranged in the left-right direction when tilted in the left-right direction depending on the degree of tilt in order to secure the size of the opening through which the DUT 7 passes. long,
When tilted in the vertical direction, the coil shape is long in the vertical direction. The passing height z is the height from the lower portion of the coil in the case of the coaxial type, and in the case of the metal detector of the present invention, the height from the lower portion of the receiving coil 5 through which the belt 1 which is the conveying means passes.

[0022]

[Table 2]

From the comparison of Table 2, the detection head of the metal detector of the present invention is arranged in the left-right direction with respect to the belt as the conveying means.
Even if it is tilted 5 degrees, the detection sensitivity is almost the same as when it is vertical, and even if it is tilted 45 degrees vertically from the vertical with respect to the belt conveyance direction, the detection sensitivity is almost the same as that of the coaxial type. I understand.

[0024]

As described above, according to the present invention, the transmitting coil and the receiving coil are arranged in substantially the same plane, and the object to be measured passes through the openings of the transmitting coil and one receiving coil. Therefore, we were able to realize a metal detector with high detection sensitivity that has never been seen before.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing a fourth embodiment of the present invention.

FIG. 5 is a diagram showing a fifth embodiment of the present invention.

FIG. 6 is a diagram showing a sixth embodiment of the present invention.

FIG. 7 is a diagram showing a seventh embodiment of the present invention.

FIG. 8 is a diagram showing an eighth embodiment of the present invention.

FIG. 9 is a diagram showing an embodiment of a method of realizing a detection head according to the present invention.

FIG. 10 is a diagram showing a configuration of a facing metal detector which is a conventional technique.

FIG. 11 is a diagram showing a configuration of a coaxial metal detector that is a conventional technique.

FIG. 12 is a diagram showing a configuration of a horizontal single-sided metal detector that is a conventional technique.

[Explanation of symbols]

 1 Belt as a Conveying Device 2 Roller 3 Roller 4 Transmission Coil 5 Reception Coil 6 Reception Coil 7 DUT 8 Object to be Measured 8 Mixed Metal 9 Reference Signal Generator 10 Filter 11 Power Amplifier 12 Differential Amplifier 13 Phase Shifting Circuit 14 First Detection Circuit 15 Second detection circuit 16 Band filter 17 Band filter 18 Amplifier 19 Amplifier 20 A / D converter 21 A / D converter 22 Judgment means 23 Insulating substrate

Claims (1)

[Claims] 1. A transporting means (1) for transporting an object to be measured, and an opening (4a) arranged in a plane that interrupts a transportation path of the transporting means and through which the object to be measured passes. Two transmitter coils (4) and in substantially the same plane as said plane,
A metal detector, one of which comprises at least two receiving coils (5, 6) with an opening (5a) through which the object to be measured passes, the metal detector detecting metal contained in the object to be measured. .