JPH0820523B2 - Metal detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application of the Present Invention> The present invention relates to a metal detection method for detecting a metal mixed in food or the like.

<Prior Art> This type of metal detector is configured to pass an object to be inspected in a magnetic field, detect the influence of the object to be inspected on the magnetic field, and inspect for the presence of mixed metal.

This detection method varies greatly depending on the product to be inspected, and if non-ferrous metal such as aluminum foil is used for the packaging of the inspected product, it is necessary to detect eddy currents in the non-ferrous metal and detect the mixed iron. , A detection method using a DC magnetic field is used.

<Problems to be Solved by the Invention> However, in the detection by the DC magnetic field as described above, although the mixing of iron can be detected satisfactorily, the detection sensitivity to the mixing of nonferrous metal is very poor, and the shape of the mixed nonferrous metal is considerably large. There was a problem that it could not be detected unless it was big.

In particular, in recent years, many confectioneries and the like packaged with a packaging material in which aluminum is vapor-deposited are produced, which makes it more difficult to find a mixed metal. Therefore, there has been a strong demand for a highly sensitive detector capable of accurately detecting contamination even in an article packaged with a packaging material vapor-depositing a non-ferrous metal.

The present invention solves this problem, particularly even in the case of an inspection object packaged with a non-ferrous metal vapor deposition material such as an aluminum vapor deposition material, a metal capable of highly sensitively detecting any mixed iron or non-ferrous metal. The purpose is to provide a detector.

<Means for Solving the Problems> In order to solve the above problems, the metal detection method of the present invention is configured to generate an AC magnetic field in a passage path of an inspection object packaged with an aluminum vapor deposition packaging material and induce the AC magnetic field. The induced signal is synchronously detected by a synchronous detection signal based on an excitation signal that is generating the AC magnetic field, and in the inspection object packaged with an aluminum vapor deposition packaging material that passes through the AC magnetic field by the detection output. A metal detection method for detecting mixed metal, wherein the eddy current loss of the aluminum vapor-deposited packaging material does not increase rapidly.
A signal of z units is used as the excitation signal, and the synchronous detection signal is set so that the influence of the eddy current loss of the aluminum vapor deposition packaging material passing through the AC magnetic field is minimized.

<Operation> Therefore, according to the present invention, when the inspection object packaged with the aluminum vapor deposition packaging material passes through the AC magnetic field,
The effect of the eddy current loss is small, and it is possible to detect with high sensitivity the ferrous and non-ferrous metals mixed in the inspected product packaged with this aluminum vapor deposition packaging material.

<Embodiment of the Present Invention> (FIGS. 1 to 3) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a metal detector which is an embodiment of the present invention.

In the figure, the magnetic field generation unit 1 divides the signal from the oscillator 2 by the frequency divider 3, converts the divided output into a sine wave by the filter 4, and sends this output to the transmission coil 5 as an excitation signal, An alternating magnetic field is generated from the transmission coil 5.

The frequency of the excitation signal of the transmission coil 5 is generally used in this type of device so that metal detection can be performed on an article packaged with a packaging material in which a nonferrous metal is vapor-deposited on a material such as paper or vinyl. It is set to a frequency much lower than the frequency (several 100 KHz), for example, several 10 KHz. This is because the influence of non-ferrous vapor deposition materials such as aluminum on the magnetic field frequency is
As shown in the figure, the higher the frequency, the more rapidly it increases due to the eddy current loss, so this effect is small and the mixed non-ferrous metal can be detected well.

Reference numeral 6 denotes a magnetic field detection unit arranged at a position for receiving an AC magnetic field from the transmission coil 5, and a differentially connected reception coil.
A resonant circuit is formed by 7a, 7b, the variable resistor VR and the capacitor C ₀ . The resonance frequency is substantially tuned to the frequency of the excitation signal, and is adjusted so that the differential output becomes zero in the normal state without the inspection object W.

Reference numeral 8 is a phase adjustment circuit that changes the phase of the received signal by switching the plurality of capacitors C _{1 to} C _{n with} the switch 9 to slightly change the resonance frequency of the magnetic field detection unit 6.

The phase adjusting circuit 8 is adjusted in advance so that the aluminum-deposited packaging material for packaging the inspected product W has a minimal influence on the AC magnetic field.

That is, as shown in FIG. 3, the influence of the aluminum vapor deposition on the AC magnetic field of the packaging material is in a certain phase range (φ ₁ to φ ₂ , φ ₃ to
φ ₄ ) becomes very small, and the range becomes wider as the excitation frequency becomes smaller, and the phase adjustment circuit 8 is adjusted in advance based on the experimental result, and the phase difference is set to be the center φ _0. .

The reference numeral 10 synchronously detects the received signal from the phase adjusting circuit 8 with the synchronous detection signal based on the excitation signal in the detection circuit 11, holds the peak level of this detection output in the peak hold circuit 12, and holds it in the comparison circuit 13. This is a discriminating circuit for discriminating the presence or absence of mixed metal by comparing the output with a reference level (limit value) preset in the setting device 14.

When the inspected product W wrapped with the aluminum-deposited wrapping material is passed between the transmitter coil 5 and the receiver coils 7a and 7b of the metal detector configured as described above, the level of the received signal changes and The detection output from the circuit 11 varies slightly due to the influence of the contents of the inspected product W and the packaging material of aluminum vapor deposition as shown in FIG. 4 (a). The amount of change is less than or equal to the limit value as described above.

Here, when metal is mixed in the inspection object W,
As shown in FIG. 4 (b), when the metal mixed portion passes through, the detection output is greatly increased under the influence of the mixed metal and the level exceeding the limit value of the setter 15 is held in the peak hold circuit 12. Therefore, the comparison circuit 13 outputs a determination signal notifying that the mixed metal is mixed.

In the conventional detection method using a DC magnetic field, the limit was to detect a stainless ball (SUS304) having a diameter of 6 mm as the mixed metal, but the detector of this embodiment detects a slenderless ball having a diameter of 3 mm. I was able to.

<Other Embodiments of the Present Invention> In the above embodiments, the phase adjusting means adjusts the phase of the received signal by slightly changing the resonance frequencies of the receiving coils 7a and 7b. The present invention is not limited to this, and even if the phase of the excitation signal for the detection circuit 11 is adjusted by the phase shift circuit, it is equivalent to changing the phase of the received signal, and the same effect can be obtained.

Further, in the above-mentioned embodiment, the receiving coils 7a and 7b are differentially connected as means for detecting the magnetic field, and the variable resistor VR is adjusted so that the output is normally zero. May be a magnetic field detecting means in which one receiving coil is arranged along the passing direction of the coil and is connected in parallel with a capacitor to form a resonance circuit, or another magnetic field detecting sensor such as a hall element is used in addition to the coil. May be.

<Effects of the Present Invention> As described above, the metal detection method of the present invention uses a signal of several tens KHz in which the eddy current loss of the aluminum vapor deposition packaging material does not increase rapidly as an excitation signal, and performs synchronization based on this excitation signal. Since the detection signal is set to minimize the effect of eddy current loss on the aluminum vapor deposition packaging material that passes through the AC magnetic field, it has been difficult to detect metal by the AC magnetic field. It is possible to detect with high sensitivity ferrous and non-ferrous metals mixed in the inspected product packaged with.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the degree of magnetic field influence on the frequency of nonferrous metals. FIG. 3 is a characteristic diagram showing the degree of magnetic field influence on the phase of the non-ferrous vapor deposition material obtained by the experiment. FIGS. 4A and 4B are signal diagrams showing the operation of the embodiment. 1 ... Magnetic field generator, 6 ... Magnetic field detector, 8 ... Phase adjustment circuit, 10 ... Discrimination circuit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-64-54281 (JP, A) JP-A-62-32382 (JP, A) JP-A-51-141655 (JP, A) JP-B-54- 20877 (JP, B1)

Claims (1)

[Claims] 1. An AC magnetic field is generated in a passage path of an inspected product packaged with an aluminum vapor deposition packaging material, and an induced signal induced by the AC magnetic field is synchronized based on an excitation signal generating the AC magnetic field. A metal detection method for synchronously detecting a detection signal and detecting the metal mixed in an inspected product packaged with an aluminum vapor deposition packaging material that passes through the alternating magnetic field by the detection output, wherein the aluminum vapor deposition package Material eddy current loss does not increase rapidly 10s KHz
Using a table signal as the excitation signal, the synchronous detection signal is set so that the influence of the eddy current loss of the aluminum vapor-deposited packaging material passing through the AC magnetic field is minimized. Method.