JPS5940287A - Apparatus for detecting metal - Google Patents

Abstract

PURPOSE:To simultaneously detect both of iron and a nonferrous metal in high sensitivity by using one detection head, by using two magnetic fields different in frequency. CONSTITUTION:Two sets of alternating magnetic fields different in frequency are generated from the transmission coil P of a detection head 14 through a drive transformer B by drive signals different in frequency from oscillators 11a, 11b corresponding to the kind of an object to be inspected and induction voltages E1, E2 corresponding to iron and a nonferrous metal present in the object W to be inspected passing between coils P, S1 and S2 are generated respective receiving coils S1, S2 of the head 14. In this case, a non-equilibrium signal corresponding to the present substances is generated from a balance circuit 15 to be separated into frequency components of respective oscillators 11a, 11b by a frequency divider 17 and iron and the nonferrous metal are respectively detected by a phase detector or a filter and comparators 18a, 20a, 22a, 18b, 20b and 22b. By this constitution, one detection head is used to simultaneously perform high sensitivity detection of iron and the nonferrous metal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal detection device for detecting metal mixed in an object to be inspected, and more particularly to a metal detection device capable of simultaneously detecting ferrous and non-ferrous metals with high sensitivity using one detection head.

A metal detection device used for the purpose of detecting metal mixed into a product is generally based on the detection principle shown in FIG.

In Fig. 1, numeral 1 denotes a detection head, which includes a transmitting coil P that generates an alternating magnetic field by receiving an alternating signal from an oscillator, and a magnetic field line of the alternating magnetic field produced by the transmitting coil P that is placed opposite to the transmitting coil P in equal amounts. It includes two receiving coils S1 and S2 arranged so that the induced voltages E1 and E2 generated by the intersecting alternating magnetic fields are equal. A device (not shown) transports the object W to be inspected at a predetermined speed between the transmitting coil P and the receiving coils s1 and s2 arranged in this way from one receiving coil S1 to the other receiving coil s2. Transport by. If metal is mixed into the object W to be inspected, the magnetic lines of force will change due to the metal. That is, if iron is mixed in the object W to be inspected, as shown in FIG. ] The number of lines of magnetic force that intersect with the receiving coil S1 increases, and the induced voltage E1 increases, and becomes larger than the induced voltage F2 of the other receiving coil S2. When non-ferrous metals are mixed in, eddy currents flow in the non-ferrous metals as shown in Figure 3, and electromagnetic flux is consumed as energy of the eddy currents, reducing the number of magnetic saw wires that intersect with one receiving coil S1. , the induced voltage E1 decreases, and the induced voltage E of the other receiving coil S2 decreases.
It will be less than 2.

In this way, if metal is mixed in the object W to be inspected, the first and second receiving coils S1
, S2, and the differential voltage between them is output as an unbalanced signal to detect metal.

FIG. 4 is a diagram schematically showing the configuration of a conventional metal detection device based on the above detection principle. That is, from the oscillation 'a2, a signal of a predetermined frequency is output to the transmitting coil P of the detection head 1, causing the transmitting coil P to generate an alternating magnetic field. Inspected object W
is moved between the transmitting coil P and the first and second receiving coils $1 and S2 by the 1lrt3 mechanism. If metal is mixed in the object W to be inspected, during this movement, the induced voltage E1 in the first and second receiving coils S1, S2,
A difference occurs in E2, and this difference signal is outputted from the balance circuit 3 as an unbalanced signal.

Among metals, in the case of iron and non-ferrous metals, the above-mentioned I,
= The opposite phenomenon occurs regarding fluctuations in induced voltage, and the relationship between the phase of the high-frequency current applied to the transmitter coil and detection sensitivity is the best point for metal sensitivity in the case of iron and the detection sensitivity for non-ferrous metals. It is known that the phase of the best point is shifted by about 90'. Therefore, this unbalanced signal is sent to the two phase detectors 5a and 5b via the amplifier 4, and the unbalanced signal is detected by shifting the phase by 90' from each other.
An iron detection signal is output based on the detection output of a, and 90'
A non-ferrous metal detection signal is output based on the detected output of the advanced phase detector 5b.

In this manner, the conventional metal detection device uses one detection head and drives its transmitting coil with one frequency 3- drive signal to simultaneously detect ferrous and non-ferrous metals.

It is well known that the sensitivity of metal detection changes depending on the frequency of the drive signal that drives the transmitting coil, but the material itself of the object to be inspected can also affect the lines of magnetic force (material effect). However, since the degree of this material effect also changes depending on the frequency, the optimum frequency for detecting iron is different from the optimum frequency for detecting non-ferrous metals.

However, in conventional metal detection devices, one frequency is selected to drive the transmitting coil so that both ferrous and non-ferrous metals can be detected with high sensitivity, with the least effect on the material of the object to be inspected. However, since the optimal frequency for sea urchin detection and the frequency with the least material effect are different for ferrous and non-ferrous metals, even if one frequency is selected, the detection sensitivity of the other is different. Increasing the detection sensitivity of the other one deteriorates, making it difficult to achieve high sensitivity for both ferrous and non-ferrous metals. For this reason, 4-2 detection heads were provided, each detecting ferrous and non-ferrous metals separately at different frequencies.

The object of the present invention is to solve the above-mentioned problems and provide a metal detection device that detects ferrous and non-ferrous metals with the highest sensitivity using a single detection head. For this purpose, in the present invention, one transmitting coil is simultaneously driven by driving signals of two frequencies optimal for detecting ferrous and non-ferrous metals, and the unbalanced signal from the receiving coil side is driven at the two frequencies. It is characterized in that it separates into components and outputs detection signals for ferrous and non-ferrous metals, respectively.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 5 is a block diagram schematically showing the configuration of a metal detection device according to an embodiment of the present invention.

In FIG. 5, reference numerals 11a and 11b are oscillators that output drive signals with optimal frequencies for ferrous and non-ferrous metals, respectively, depending on the type of object W to be inspected, and oscillators 12a and 12b are oscillators 1, respectively.
A voltage amplifier 13 amplifies the output signals of 1a and 11b, and a drive 1 13 drives the transmitting coil P of the detection head 14.
The transmission coil P is driven by drive signals of two different frequencies applied to the negative windings CI and C2. Reference numeral 14 denotes a detection head consisting of a transmitting coil P and two receiving coils S1 and S2 placed opposite to the transmitting coil P. They are arranged so that the lines of magnetic force of the generated alternating magnetic field intersect by equal amounts and the induced voltages E1 and F2 are equal.

A balance circuit 15 outputs the difference between the induced voltages E1 and F2 generated in the receiving coils S1 and S2 as an unbalanced signal. 16 is an AC amplifier that amplifies the unbalanced signal. Reference numeral 17 denotes a duplexer that separates the unbalanced output of the balance circuit 15 into two frequency components of two drive signals of the two oscillators 11a and 111). 18a and 18b are phase detectors for detecting ferrous and nonferrous metals, respectively, and voltage amplifiers 1 through phase shifters 19a and 19b, respectively.
Phase detector 18b is detected by the output signals from 2a and 12b.
The side is detected with a phase lead of 90° from the phase detector 18a. 20a and 20b are phase detectors 18a and 1, respectively.
a filter for removing noise caused by vibrations of the transport device for moving the object W to be inspected from the detection coil 811 or other metals near the detection coils S1 and S2;
1a and 21b are filters 20a and 20b, respectively.
Amplifiers 22a and 22h amplify the output signals of the amplifiers 21a and 21b, respectively, when the output signal levels of the amplifiers 21a and 21b exceed the set reference level.
A comparator 23 that outputs a non-ferrous metal detection signal is an OR circuit.

Next, the operation of the metal detection device having the above configuration will be explained.

The oscillators 11a and 11b output drive signals of two different frequencies, which are selected according to the type of object to be inspected and are optimal for detecting ferrous and non-ferrous metals, respectively, and are amplified by voltage amplifiers 12a and 12b, respectively. 7- is sent to the primary windings C1 and C2 of the drive 1 to lance 13. As a result, the transmitting coil P of the detection head 14
is driven at two different frequencies to generate an alternating magnetic field. When there is no metal, the lines of magnetic force due to this alternating magnetic field intersect equally across the two receiving coils $1 and S2, causing each induced voltage E.
l and F2 are equal.

Between the transmitting coil P and the two receiving coils S1 and S2,
When the inspected object W is conveyed by the conveying device in the 82 direction from Sl at a predetermined speed, if metal is present in the inspected object W, the lines of magnetic force change and the two receiving coils $1 and S
The two induced voltages E1 and F2 are no longer equal, and an unbalanced signal is generated from the balance circuit 15. The unbalanced signal from the balance circuit 15 is amplified by the AC amplifier 16, and the unbalanced signal from the balance circuit 15 is amplified by the AC amplifier 16.
J: Frequency component of oscillator 11a and oscillator 111]
The signal is separated into frequency components and sent to a phase detector 18a for detecting iron and a phase detector 181 for detecting non-ferrous metals. The phase detectors 18a and 18b detect the signals of the phase shifters 19a and 19b whose phases are different by 90 degrees from each other (the phase detector 198-b has a phase lead of 90 degrees).

The output signals of the phase detectors 18a and 18b are filtered by filters 20a and 120b, respectively, to eliminate noise caused by vibrations of the conveyance device that moves the object to be inspected, and the detection coil section 4.
Noise caused by other metals in the vicinity of is removed, amplified by amplifier circuits 21a and 21b, and
A comparison is made to see if the level is higher than a predetermined reference level, and if this level is exceeded, a detection signal for iron and a detection signal for non-ferrous metal are outputted via the OR circuit 22, respectively.

The frequency of the output j signal from each of the oscillators 11a and 11b is selected depending on the type of the object W to be inspected to a frequency at which iron and nonferrous metals are detected with the highest sensitivity.

As explained above, in the metal detection device of the present invention, the two optimal frequencies for detecting ferrous and non-ferrous metals are selected, and the transmitting coil P of one detection head 14 is simultaneously driven, and the receiving coil The unbalanced signal on the side is separated into the two frequency components, and Jζ is used to detect ferrous and non-ferrous metals respectively in the two separated signal series, so one detection head can simultaneously detect ferrous and non-ferrous metals. Both non-ferrous metals can be detected with the highest sensitivity.

[Brief explanation of drawings]

Figure 1 is a diagram showing the detection principle of the metal detection device, Figure 2 is a diagram that does not show the influence of iron on magnetic lines of force, Figure 3 is a diagram showing the influence of non-ferrous metals on magnetic lines of force, and Figure 4 is a diagram of the conventional FIG. 5 is a block diagram showing a schematic configuration of a metal detecting device. FIG. 5 is a block diagram showing an embodiment of the metal detecting device of the present invention. 11a, 111) ----- Oscillator, 12a,
12+) -...Voltage amplifier, 13...
Drive transformer, 14...Detection head, 15...
... Balance circuit, 16 ... AC amplifier,
17... Duplexer, 18a, 18b...
Phase detector, 19a, 1911... Phase shifter, 2
0a1201)...Filter, 21a, 21
b...Amplifier, 22a, 22b...Comparator, 23...OR circuit, 1]...Transmission coil, Sl, S2...・Receiving coil, El
, E2... Induced voltage, W... Test object. 11- Figure 1 Figure 2 Figure 3 EI E2

Claims (1)

[Claims] a transmitting coil, a drive circuit that drives the transmitting coil to generate an alternating magnetic field, and first and second receiving coils arranged to receive the magnetic field generated by the transmitting coil;
a balance circuit that outputs an unbalanced signal based on fluctuations in the induced voltage of the first and second receiving coils caused by metal mixed in the object to be inspected passing through the magnetic field; In a metal detection device comprising a detection circuit that outputs a detection signal: the drive circuit drives the transmitting coil with drive signals of two different frequencies, and the detection circuit detects the two frequency components from the unbalanced signal. A metal detection device is characterized in that it extracts and outputs detection signals for ferrous and non-ferrous metals.