JPH09304546A - Method and apparatus for detection of metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detection apparatus by which a mixed metal existing inside an object to be inspected can be detected with high sensitivity regardless of a magnetic metal or a nonmagnetic metal even in the case of the object to be inspected, which is wrapped with a nonmagnetic metal whose thickness is comparatively thick such as an aluminum foil or the like. SOLUTION: The apparatus is provided with an oscillator 1 which outputs an AC signal, with a transmitting coil 2 which generates an AC magnetic field by using the AC signal from the oscillator 1, with a first receiving coil 3a and a second receiving coil 3b which are wound coaxially with the transmitting coil 2 and which induce unbalanced signals due to the existence of a metal in an object W, to be inspected, passing inside a magnetic field generated by the transmitting coil 2, with a detection circuit 7 which detects the unbalanced signals from the first and second receiving coils 3a, 3b and with a phase shifter 8 which changes the phase of the AC signal from the oscillator 1 and which supplies a detection signal to the detection circuit 7. In this case, a mechanism 5 which adjusts positions of the transmitting coil 2 and the receiving coils 3a, 3b, which are wound coaxially, in such a way that the center of a nonmagnetic metal as the wrapping material of the object W to be inspected is passed through a part near its axial center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detecting method and a metal detecting apparatus, and more particularly, to an object to be inspected on the basis of a change in the magnetic field caused by the metal in the object to be inspected by passing the object to be inspected in a magnetic field. The present invention relates to a metal detection method and a metal detection device for detecting a metal in a metal.

[0002]

2. Description of the Related Art Conventionally, the magnetic field generated by the magnetic field generating means is passed through the object to be inspected, and the unbalanced outputs of the two magnetic field detecting means by the metal in the object to be inspected cause the object to be inspected. Metal detection devices for detecting the metal inside are well known.

In this type of metal detecting device, in order to detect a metal in an object to be inspected which is wrapped with a non-magnetic metal foil such as chocolate, an alternating current in which the directions of magnetic force lines are alternately inverted. When a magnetic field is used, the unbalanced output of the aluminum foil itself, which is the packaging material, becomes large, making it difficult to detect minute metal in the DUT. It has been generally performed to detect a metal in an object to be inspected by using (Japanese Unexamined Patent Publication No. 51-141655, etc.).

However, in the metal detecting device using the DC magnetic field as described above, although the magnetic metal such as iron has a high magnetic permeability, the detection can be performed well, but the non-magnetic substance is not detected. Metal, such as aluminum, copper, and stainless steel, has a very poor detection sensitivity because eddy currents do not flow like AC magnetic fields, and it cannot be detected unless the size of the mixed non-magnetic metal is considerably large. There was a problem to say.

Therefore, in recent years, a metal detection method has been proposed in which the presence or absence of mixed metal is detected by using an alternating magnetic field even in an object to be inspected packaged with a non-magnetic metal such as an aluminum vapor deposition material (special feature). Kaihei 2-262089 etc.). This metal detection method uses a product that gives a phase difference between a signal that generates an AC magnetic field of about several tens of kHz and a reception signal received by a magnetic field detection unit disposed at a position receiving the AC magnetic field to the reception signal. A method of adjusting using a known means that it is set in advance to a value at which the influence is small, and passing an inspected object wrapped with a nonmagnetic metal in an AC magnetic field in this state to detect the presence of mixed metal It is.

However, in such a metal detection method,
As a result of the test / research conducted by the applicant of the present application, it was found that the detection sensitivity of the mixed metal in the inspected object varies greatly depending on the position of the inspected object passing through the magnetic field. That is, an object to be inspected packaged with a relatively thick non-magnetic metal such as aluminum foil is placed coaxially with a transmitter coil for generating an alternating magnetic field and a position for receiving this alternating magnetic field. A position that is largely deviated from the axis with respect to the receiving coil, for example, a position that is 1/2 the distance from the axis to the lower end of the coil (a position that is 1/4 of the coil height) is passed as shown in FIG. in case of,
Even after the phase of the detection signal is adjusted by the phase shift circuit to the phase value where the influence of the non-magnetic metal, which is the packaging material of the object to be inspected, is the packaging material, as shown by the chain line in FIG. The output of non-magnetic metal after detection is quite large (X in the figure
It has been found that there is a problem that the detection sensitivity of the mixed metal in the object to be inspected is extremely deteriorated.

Further, in the above-described method for detecting a metal using an alternating magnetic field, a non-magnetic metal having a relatively large thickness such as an aluminum foil has an effect of shielding the alternating magnetic field.
In an alternating magnetic field with a high frequency of about several tens of kHz as shown in 262089, several tens of nanometers are required like an aluminum vapor deposition material.
Transmission is possible with a non-magnetic metal of thickness m,
In the case of a non-magnetic metal having a thickness of about 10 μm, such as aluminum foil, it cannot easily pass through, and even if foreign metal is mixed inside, a sufficient magnetic field is applied to this foreign metal. It was found that there is also a problem that the unbalanced output due to the metallic foreign matter itself becomes small because it is not present, and its detection becomes difficult.

The present invention has been made in view of the problems of the above-existing conventional metal detecting device and metal detecting method, and its object is to provide a relatively thick non-magnetic material such as aluminum foil. An object of the present invention is to provide a metal detection method and a metal detection device capable of detecting a mixed metal existing inside thereof with high sensitivity regardless of whether it is a magnetic metal or a non-magnetic metal, even for an inspection object packaged with metal. .

[0009]

As a result of repeated tests and studies to achieve the above-mentioned object, the inventors of the present invention have found that the center of a non-magnetic metal, which is a packaging material for an object to be inspected, is wound coaxially. When passing the object to be inspected so that it passes near the axis of the transmitting coil and the receiving coil, the output after detection of the non-magnetic metal, which is the packaging material after adjusting the phase difference, is very small. The present invention has been completed based on the knowledge that an AC magnetic field having a frequency of 1 kHz or less can easily pass through a relatively thick non-magnetic metal such as an aluminum foil.

That is, according to the present invention, the phase difference between the signal sent to the transmitting coil for generating an alternating magnetic field and the receiving signal received by the receiving coil wound coaxially with the transmitting coil is
In the metal detection method for detecting the presence or absence of mixed metal in the object to be inspected packaged with the non-magnetic metal metal in a state where the influence of the non-magnetic metal metal that is the packaging material is small after detection, A metal detection method performed by passing a test object such that the center of a non-magnetic metal that is a packaging material of the test object passes near the axes of the coaxially wound transmission coil and reception coil. And Further, according to the present invention, an oscillator for outputting an AC signal, a transmission coil for generating an AC magnetic field by the AC signal from the oscillator, a coil wound coaxially with the transmission coil, and passing through a magnetic field generated by the transmission coil. First and second receiving coils that induce an unbalanced signal due to the presence of metal in the device under test, a detection circuit that detects the unbalanced signals from the first and second receiving coils, and the oscillator In a metal detection device equipped with a phase shift circuit for changing the phase of an AC signal and supplying a detection signal to the detection circuit, the positions of the coaxially wound transmitter coil and receiver coil are packaged in an object to be inspected. The metal detecting device is provided with a mechanism for adjusting the position so that the center of the non-magnetic metal that is the material passes near the axis of the metal.

According to the metal detecting method and the metal detecting apparatus of the present invention described above, the object to be inspected, which is packaged with a relatively thick non-magnetic metal such as aluminum foil, is inspected by using an alternating magnetic field. The metal detection method and the metal detection device can suppress the detection of the unbalanced output due to the aluminum foil itself which occurs in the case as much as possible, and can detect the metal foreign matter mixed in the inspection object with high sensitivity.

That is, according to the present invention, the center of the non-magnetic metal, which is the packaging material for the object to be inspected, passes through the vicinity of the axes of the coaxially wound transmitting coil and receiving coil. Since the presence or absence of mixed metal is detected by passing through, the phase of the detection signal is adjusted by the phase shift circuit to the phase value that minimizes the effect of the non-magnetic metal, which is the packaging material of the object to be inspected. The output of the non-magnetic metal itself after detection is extremely small, and the output due to only the metallic foreign matter mixed in the inspected object can be greatly detected, so it is highly sensitive to the presence or absence of metallic foreign matter mixed in the inspected object. A metal detection method and a metal detection device that can be detected by.

The AC magnetic field applied to the object to be inspected in the present invention is an AC magnetic field of 1 kHz or less. This is because an AC magnetic field of 1 kHz or less can easily pass through a relatively thick non-magnetic metal such as aluminum foil, and a sufficient magnetic field can be applied to the mixed metal present inside. The reason is that the disturbance of the magnetic field due to the mixed metal can be largely detected, and the minute mixed metal can be found.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Here, FIG. 1 is a block diagram showing an embodiment of a metal detecting device according to the present invention. In FIG.
Is an oscillator that outputs an AC signal of 1 kHz or less, and 2 is a transmission coil connected to the oscillator 1. In the alternating magnetic field of the transmitting coil 2, two receiving coils 3a and 3b coaxially wound with the transmitting coil 2 are arranged so that magnetic fluxes are equally linked. The transmission coil 2 and the reception coils 3a and 3b are housed in a commonly used square-shaped detection head 4, and the detection head 4 is vertically movable by a height adjusting mechanism 5. Has been done.

6 is a differential amplifier for amplifying the electromotive force difference induced in the transmission coils 3a, 3b, 7 is a detection circuit for synchronously detecting the output signal from the differential amplifier 6, and 8 is a signal from the oscillator 1. A phase shift circuit that changes the phase of the AC signal and supplies the detection signal to the detection circuit 7, and 9 is a filter circuit that passes only the low frequency band determined by the passing speed of the inspection object from the output signal of the detection circuit 7. Reference numeral 10 is a determination means for outputting a metal detection signal when the voltage level of the output signal from the filter circuit 9 is equal to or higher than the reference level. Also, 1
Reference numeral 1 is a conveying means for allowing the object W to be inspected to pass through the AC magnetic field generated from the transmitting coil 2.

In the metal detecting device constructed as described above, the oscillator 1 oscillates an alternating current signal having a frequency of 1 kHz or less, which causes the transmitting coil 2 to generate an alternating magnetic field having a frequency of 1 kHz or less. Usually, the transmission coil 2
The voltage and phase of the AC signal generated in the two receiving coils 3a and 3b receiving the AC magnetic field from are adjusted to be equal, and the output from the differential amplifier 6 is zero.

Here, as shown in FIG. 2, the object W to be inspected, which is packaged with a non-magnetic metal such as aluminum foil, is wrapped around the center of the non-magnetic metal that is the packaging material. When the height adjustment mechanism 5 adjusts the position of the detection head 4 so that it passes near the axis of the transmission coil 2 and the reception coils 3a and 3b, metallic foreign matter is mixed into the object W to be inspected. Even if it is not, the magnetic flux changes due to the influence of the non-magnetic metal that is the packaging material, and an unbalanced signal is output from the differential amplifier 6. The unbalanced signal has an oscillation frequency that is not the packaging material. The modulated signal is modulated by the passage speed of the magnetic metal.

This modulated signal is detected and demodulated by the detection circuit 7 and output to the judgment means 10 via the filter circuit 9. The influence of the modulated signal greatly changes as shown by the solid line in FIG. 3 depending on the phase shift value of the phase shift circuit 8 which supplies the detection signal to the detection circuit 7. Therefore, the determination unit 10 adjusts the phase of the detection signal supplied to the detection circuit 7 by the phase shift circuit 8 so that the influence of the modulated signal by the packaging material of the inspection object W is minimized.

After the phase of the detection signal supplied to the detection circuit 7 is adjusted in this way, the carrier means 11 is operated to operate the object W to be inspected packaged with the same kind of non-magnetic metal at the time of the phase adjustment. Similarly to the above, the transmitter coil 2 and the receiver coil 3 in which the center of the non-magnetic metal that is the packaging material is coaxially wound.
The metal foreign matter in the object W to be inspected is conveyed by being conveyed so as to pass through the vicinity of the axes of a and 3b.

The most characteristic feature of the present invention configured as described above is that the center of the non-magnetic metal, which is the packaging material for the object to be inspected, is
It is to detect the presence or absence of mixed metal by passing the inspected object so as to pass through the vicinity of the axial center of the transmitting coil and the receiving coil wound on the same axis. When the object to be inspected is passed through in such a state, the output of the non-magnetic metal, which is the packaging material after the phase difference is adjusted as shown in FIG. It is possible to detect only the output due to the metallic foreign matter mixed in the metal, and it is possible to detect even minute mixed metal. Here, in comparison with the applicant of the present invention, it is generally performed in the case where an object to be inspected wrapped with an aluminum foil having a thickness of about 10 μm is passed near the axis of the coil as in the present invention described above. Compared with the case of passing the position of 1/2 the distance from the axis to the bottom of the coil (the position of 1/4 of the coil height), it is about 30 times when passing near the axis. It was found that the sensitivity was improved. Further, it has been found that the fluctuation of the sensitivity can be suppressed to a practically acceptable level in the vicinity of the axis center which is displaced by 5% or less from the axis center of the coil.

A further feature of the present invention is that an AC magnetic field having a low frequency of 1 kHz or less is applied to the object W to be inspected and the presence or absence of mixed metal is inspected. An AC magnetic field of 1 kHz or less, as shown in FIG. 4 (a diagram of test results showing what percentage of the signal of the metal inside when the metal was put inside the aluminum foil, could be detected outside the aluminum foil), It can easily pass through a non-magnetic metal foil such as aluminum foil, and can add a sufficient magnetic field to the mixed metal existing inside, so the disturbance of the magnetic field due to the mixed metal can be detected greatly and fine mixing You will also be able to discover metals.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modifications and changes can be made within the scope of the technical idea of the present invention. is there. For example, in the above embodiment, the present invention has been described as an inspection device for an object to be inspected which is entirely packaged with a non-magnetic metal such as an aluminum foil, but for example, a milk in which the aluminum foil is used only for the lid. The present invention can also be applied to an inspection apparatus for products such as products and cup ramen in which a non-magnetic metal is used in a part of the container. However, at this time, since the non-magnetic metal that is the packaging material is the lid part, the position of the lid part is adjusted so that the center of the lid part passes near the coaxial axes of the transmitting coil and the receiving coil. Adjust the mechanism to detect the presence of mixed metals.

[0024]

As described above, according to the above-described metal detecting apparatus of the present invention, even an object to be inspected, which is packaged with a relatively thick non-magnetic metal such as an aluminum foil, exists inside thereof. There is an effect of providing a metal detection method and a metal detection device capable of detecting the mixed metal to be mixed with high sensitivity regardless of whether it is a magnetic metal or a non-magnetic metal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a metal detection method and a metal detection device according to the present invention.

FIG. 2 is a perspective view showing a passing position in the coil of the inspection object according to the present invention.

FIG. 3 is a diagram showing a difference in output after detection with respect to a phase shift value due to a difference in passing position of an aluminum foil as a packaging material in a coil.

FIG. 4 is a diagram showing a transmittance of a signal from a metal inside an aluminum foil.

FIG. 5 is a perspective view showing a passing position in a coil of an object to be inspected, which is generally performed conventionally.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 oscillator 2 transmission coil 3a, 3b reception coil 4 detection head 5 height adjusting mechanism 6 differential amplifier 7 detection circuit 8 phase shift circuit 9 filter circuit 10 determination means 11 carrier means W inspection object

Claims (4)

[Claims] 1. A phase difference between a signal sent to a transmission coil that generates an alternating magnetic field and a reception signal received by a reception coil that is wound coaxially with the transmission coil. A metal detection method for detecting the presence or absence of a mixed metal in an inspected object packaged with a non-magnetic metal in a state in which the influence of metal is set to a value that is small in advance. A method for detecting a metal, which is performed by allowing an object to be inspected to pass through such that a center of a magnetic metal passes through a vicinity of axes of a transmission coil and a reception coil which are coaxially wound. 2. The signal sent to the transmission coil is 1k.
The metal detection method according to claim 1, wherein the alternating current signal has a frequency of Hz or less. 3. An oscillator that outputs an AC signal, a transmission coil that generates an AC magnetic field by the AC signal from the oscillator, and a target that is wound coaxially with the transmission coil and that passes through a magnetic field generated by the transmission coil. First and second receiving coils that induce an unbalanced signal due to the presence of a metal in the inspection body, a detection circuit that detects the unbalanced signals from the first and second receiving coils, and an alternating current from the oscillator In a metal detection device including a phase shift circuit that changes the phase of a signal and supplies a detection signal to the detection circuit, the positions of the coaxially wound transmitter coil and receiver coil are determined by the packaging material of the object to be inspected. 2. A metal detecting device, which is provided with a mechanism for adjusting the position so that the center of the non-magnetic metal is a center of the non-magnetic metal. 4. The AC signal output from the oscillator is
The metal detection device according to claim 3, wherein the metal detection device has an alternating current signal of 1 kHz or less.