JPS6335945B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a detection device for detecting metals mixed in an object to be inspected, which detects whether or not metal is mixed in an object to be inspected (particularly food) being conveyed by a conveyor or the like. .

First, an overview of a conventionally used metal detection device will be explained with reference to FIG.

In this figure, 1 is an oscillator, 2 is a transmitting coil connected to the oscillator 1, 3a and 3b are receiving coils arranged opposite to this transmitting coil 2, and these receiving coils 3a and 3b are It is placed in the alternating magnetic field of the coil 2 and arranged so that the lines of magnetic force intersect equally.

4a and 4b indicate volumes for adjusting the phase and amplitude of the induced voltages e〓 ₁ and e〓 ₂ of the receiving coils 3a and 3b, and by adjusting these volumes 4a and 4b, usually e〓 ₁ -e It is set so that 〓 ₂ = 0.
5 is an amplifier that amplifies the differential induced voltage e〓 ₁ −e〓 ₂ ; 6
Numerals a and 6b are synchronous detectors for detecting ferrous and non-ferrous metals, 7a and 7b are filters, and 8a and 8b are discrimination circuits. Note that 9a and 9b indicate first and second phase shifters that form synchronizing signals to be supplied to the synchronous detectors 6a and 6b.

The metal detection device having such a configuration has an object W to be inspected between the transmitting coil 2 and the receiving coils 3a and 3b.
passes through and if metal is mixed in the object W to be inspected, a detection signal is generated in the discrimination circuits 8a and 8b depending on the type of metal (ferrous or non-ferrous).

To explain this point using the vector diagrams in FIG _.
e〓 ₂ is set so that e〓 ₁ −e〓 ₂ = 0 on the input side of the amplifier 5, but the test object W containing iron
passes from the direction of the arrow, first, the induced voltage e〓 ₁ of the receiving coil 3a increases to e〓' ₁ as shown in Fig. 2a, and then the induced voltage e〓 ₂ of the receiving coil 3b increases to e〓 ′ ₂
increases to Therefore, the differential induced voltage of e〓 ₁ −e〓 ₂ = e〓 _Df is input to the synchronous detector 6a, and the in-phase synchronous detection signal e〓 _F is supplied to the synchronous detector 6a. detected by.

On the other hand, when the inspected object W containing non-ferrous metals (stainless steel, aluminum, etc.) passes through, eddy currents flow in the non-ferrous metals under the influence of the alternating current magnetic field of the oscillator 1. Then, due to the influence of this overcurrent, the phases of the induced voltages e〓 ₁ and e〓 ₂ of the receiving coils 3a and 3b change.

That is, as shown in FIG. 2b, the receiving coil 3
When the phase of the induced voltage e〓 ₁ of a changes to e〓″ ₁ , the differential induced voltage e〓″ ₁ −e〓 ₂ = e〓 _DS becomes approximately 9 as shown in the figure.
Occurs at a point with a 0° phase shift. Therefore, it is almost in phase with this differential induced voltage e〓 _Df . Non-ferrous metals can be detected by performing phase detection in the synchronous detector 6b supplied with the synchronous detection signal indicated by _e〓S .

As described above, conventional metal detection devices synchronously detect both iron (magnetic material) and non-ferrous metals using phases (for example, α and β) that allow highly sensitive detection.

However, if the product to be inspected W contains moisture and salt, such as ham, the product itself is conductive, so a detection signal similar to that of the nonferrous metal to be detected will be generated. Furthermore, if the product is seaweed or sugar, the product itself contains iron, so a detection signal similar to iron (magnetic material) is generated.

Then, when detecting foreign metals contained in such products using the metal detection device described above,
There has been a problem that the detection ability is reduced because the detection signal generated by the product itself and the detection signal of the foreign metal appear synergistically with each other or cancel each other out.

This invention was made with the aim of alleviating such problems, and by adding the detection signals of two synchronous detectors in an appropriate ratio, the detection signal of the product is canceled, and only the foreign metal is detected. The present invention provides a detection device for detecting metal mixed in an object to be inspected, which outputs a detection signal.

Hereinafter, the apparatus for detecting metal mixed in an object to be inspected according to the present invention will be explained.

FIG. 3 shows a block diagram of an apparatus for detecting metals mixed in a test object, which is an embodiment of the present invention.
As in FIG. 1 described above, 11 is an oscillator, 12 is a transmitting coil, 13a and 13b are receiving coils, and 14
15 is an amplifier, 16a and 16b are synchronous detectors made of ferrous and non-ferrous metals, and 17a and 17b are filters.

18a and 18b indicate detection signal amplifiers;
Reference numerals 9a and 19b are first and second phase shifters that form signals for synchronous detection having phases (α, β) as described later.

Further, 20 is an adder, 21 is a comparator, and one input of the addition input is supplied via a voltage divider 23.

In addition, 24 is a volume for setting the comparison voltage, 2
2 is a discrimination output circuit.

Next, FIG. 4 shows the phases (α, β) of the signals for synchronous detection when performing synchronous detection, and the level of the detection signal detected at the phases.

In this figure, the solid line indicates the detection sensitivity of the product (HAM), the dotted line indicates iron, and the dashed line indicates nonferrous metal (SUS).

In other words, the synchronous detector 16a, which is set at the point where the phase is α, has the lowest sensitivity at point a for product (H), the highest sensitivity at point c for iron (Fe), and the highest sensitivity for non-ferrous metals (SUS). shows the sensitivity of point b for
The synchronous detector 16b whose phase is β (0°) has the lowest sensitivity for iron (Fe), and the lowest sensitivity for non-ferrous metals (SUS).
indicates the detection sensitivity at point e, and product (H) indicates the detection sensitivity at point d.

Therefore, when the iron ball passes between the transmitting coil 12 and the receiving coils 13a and 13b, the output of the synchronous detector 16a whose phase is α becomes Fe( A detection signal shown in α) is obtained, and the output of the synchronous detector 16b whose phase is β is approximately 0. In addition, in the case of a non-ferrous metal ball, the synchronous detector 16a with a phase of α outputs a small detection signal SUS(α) as shown in FIG.
synchronous detector 16b whose phase is β (opposite to the case of )
Then, the detection signal SUS(β) corresponding to point e is output.

Similarly, for product (H), as shown in C, the detection signal H(α) at the lowest sensitivity point a is sent to the phase α synchronous detector 16a, and the detection signal H(β) is sent to the β phase synchronous detector 16b. A detection signal is output. However, in this case, as can be seen from Figure 4, H(β)≫H(α)
It is becoming.

From the above various detection signals, when a product containing iron passes through, the detection signal Fe+H has a smaller amplitude than the case of only iron balls, as shown in the composite waveform 2.
(α) is obtained by the α-phase synchronous detector 16a, and in the case of a conventional metal detection device, the detection sensitivity is lowered, but in the detection device for metal mixed in the object to be inspected of the present invention, in the adder 20, α phase synchronous detector 1
6a and the detection signal of the β-phase synchronous detector 16b are added together, so in case 2, the product detection signal H(β) is divided and added to detect the product. The signal H(α) is canceled, and as a result, the output of the adder 20 is Fe(α+
β) Detection signal Fe of iron ball only as shown in the waveform
(α) will be obtained. Therefore, by inputting this signal to the comparator 21 and comparing it with the reference signal, the discrimination output circuit 22 is operated, and the presence or absence of iron can be detected.

In this way, in the case of a mixed detection signal of product and iron,
Depending on the position of the iron ball within the product, the amplitude may be small or large (not shown), and the detection ability of conventional detection devices for metals mixed in the object to be inspected has decreased. However, in the metal detection device of the present invention, the β-phase synchronous detection output when detecting a product is in reverse phase and its amplitude is large, and this detection signal H(β) is divided into voltages, Since the configuration is such that it is added to the output of the α-phase synchronous detector 16a, only the product detection signal can be canceled, and only the iron detection signal Fe(α) can now be detected.

Furthermore, even if the foreign metal in the product is non-ferrous,
Although detailed explanation is omitted, the product detection signal H (β
+α) becomes zero, so only the non-ferrous detection signal is obtained (in the case of non-ferrous metals, the ratio of the α phase detection level at point b and the β phase level at point e is not large compared to the product, so the waveform As shown in (b), the detection signal is not canceled even after being added.
SUS (α+β) is obtained. ).

Therefore, the partial pressure ratio of the voltage divider 23 is adjusted according to the sensitivity of the product (sensitivity difference between ham, sausage, etc.) as described above, and the detection signal H of the product is
(α+β) is set to be zero.

As explained above, the device for detecting metal mixed in an object to be inspected according to the present invention can cancel the detection signal related to the product by adding the detection signal in an appropriate ratio among the detection signals synchronously detected in two phases. With this configuration, only foreign metals (ferrous and non-ferrous metals) contained in the product can be properly detected.

Therefore, even if the product itself contains iron or salt that exhibits conductivity, it has the advantage that these effects can be reduced and more accurate detection operations can be performed.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an outline of a conventional metal detection device, Fig. 2 a and b are vector diagrams explaining the detection operation, and Fig. 3 is an embodiment of the detection device for metal mixed in an object to be inspected according to the present invention. FIG. 4 is a diagram showing the relationship between the detection level and detection phase of objects to be inspected (products: ferrous and non-ferrous), and FIG. 5 is a waveform chart of detection signals of various objects to be inspected. In the figure, 11 is an oscillator, 12 is a transmitting coil, 13
a, 13b are receiving coils, 14a, 14b are adjustment volumes, 15 is an amplifier, 16a, 16b
is a synchronous detector, 17a and 17b are filters, 18
a and 18b are amplifiers, 19a and 19b are first and second phase shifters, 20 is an adder, and 23 is a voltage divider.

Claims (1)

[Claims] 1. A transmitting coil excited by an alternating current signal, intersecting with the magnetic field of the transmitting coil, and arranged so that the induced voltage changes in response to the object to be inspected passing through.2
a first and second synchronous detector that detects a difference signal between signals induced in the two receiving coils; a first synchronous detection signal;
a phase shifter that supplies the first and second synchronous detectors with a synchronous detection signal and a second synchronous detection signal having a different phase; an adder that cancels out the detection signal component of the object to be inspected by adding the detection outputs of the objects at a predetermined ratio; and a discrimination circuit that determines the presence or absence of metal mixed into the object from the output signal of the adder. 1. A detection device for metals mixed in an object to be inspected, comprising: