JPS5960276A - Metal detector - Google Patents

Abstract

PURPOSE:To enable adequate detection of foreign metal contained in a product by adding detection signals pertaining to the product at an adequate ratio to cancel among those detection signals from a synchronous detection in two phases. CONSTITUTION:As a product mixed with iron passes, a detection signal Fe+H (alpha) in (d) is obtained from a synchronous detector 16a, which previously lowered the detection sensitivity. In this equipment, an adder 20 is provided to add the output of the synchronous detector 16a in alpha phase and a signal obtained by voltage division of a detection signal of a synchronous detector 16b in beta phase. This cancels the detection signal H(alpha) of the product in the case of (d) by adding the detection signal H(beta) of the product once divided and the detection signal Fe(alpha) of a steel ball alone is obtained at the output of the adder 20 as shown by the Fe(alpha+beta) waveform. Therefore, the signal is inputted into a comparator 21 to be compared with a reference signal and a discrimination output circuit 22 is operated to detect the presence of iron.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal detection device for detecting whether or not metal is mixed in an object to be inspected, particularly food, being transported 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 IK, and 3a and 3b are transmitting coils 2.
The receiving coils 3a and 3b are placed in the alternating magnetic field of the transmitting coil 2,
They are arranged so that their lines of magnetic force intersect equally.

4a and 4b are induced voltages of the receiving filters 3a and 3b;
, ; indicates a volume for adjusting the phase and amplitude of , ; By adjusting these volumes 4a and 4b, normally, -
It is set to be 52-0. 5 is differential induced voltage;
, ,; , 6a and 6b are synchronous detectors that detect iron and non-ferrous metals respectively, 7a and 7b are filters, and Qa and 8b are discrimination circuits. Note that 9a and 9b are the first synchronous signals that are supplied to the synchronous detectors 6a and 6b. A metal detection device consisting of a circle 414 indicating a second phase shifter includes a transmitting coil 2
．． and the object W to be inspected passes between the receiving coils 3a and 3b,
When metal is mixed in the object W to be inspected, detection signals are generated by the discrimination circuits 8a and 8bK depending on the type K of the metal (ferrous or non-ferrous).

To explain this point using the vector diagrams in FIGS. 2(a) and 2(b), normally the induced voltages 5,
, , ;2 is at the input end of the amplifier 50 ;, ;,
5 traps are set so that = 0, but when the inspected object W containing iron passes from the direction of the arrow, first, as shown in Fig. 2 (a)
As shown in Figure 1, the induced voltage in the receiving coil 3a increases by I, and then the induced voltage 2 in the receiving coil 3b increases dramatically. Therefore, the differential induced voltage 81', -=carO is input to the synchronous detector 6a, and detected by the in-phase synchronous detection signal supplied to the synchronous detector 6a.

On the other hand, when the inspected object W containing nonferrous metals (stainless steel, aluminum, etc.) passes through, it is affected by the alternating current magnetic field of the oscillator 1, and an eddy current flows in the nonferrous metal C1. , the phase of the induced voltage of the receiving coil 3a+31>;, le, changes.

That is, as shown in FIG. 2(b), the receiving coil 3a
When the phase of the induced voltage also changes to τ, the differential induced voltage 〉 = ゎf is generated at a point out of phase by approximately 90° as shown in the figure. Therefore, this differential induction cylinder, the pressure e
It is almost the same phase as of.

Non-ferrous metals can be detected by 1 degree by performing phase detection in the synchronous detector 6b supplied with the synchronous detection signal shown in FIG.

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.

1) and foreign metals contained in such products using the metal detection device described above, the detection signals generated by the product itself (No. 8 and foreign metal detection signals appear synergistically with each other). There was a problem in that the detection ability deteriorated because the two components interacted with each other or canceled each other out.

This invention was made with the aim of reducing the problem t1, and by reducing the detection signals of two synchronous detectors at an appropriate ratio, product detection 1.1 can be canceled. The present invention provides a metal detecting device which outputs a detection signal representing a metal with a η′-end.

The metal detection device of the present invention will be explained below.

FIG. 3 shows a block diagram of a metal detection device showing one embodiment of the present invention.
12 is an oscillator, 12 is a transmitting coil, and 13a.

131] is a receiving coil, 14a and 14b are adjustment volumes, 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;
91) is the first . k] with the second phase shifter.

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

24 is a volume for setting a comparison voltage, and 22 is a discrimination output circuit.

Next, when performing synchronous detection, the phase of the signal for synchronous detection (
α, β) and the level of the detection signal detected at their phase are shown in FIG.

In this figure, the solid line indicates the detection sensitivity of the product (...), the dotted line indicates iron, and the one-dot chain line indicates nonferrous metal (S OS ).

1, that is, a synchronous detector 16 whose phase is set at a point α.
a is the lowest sensitivity point a for product (11), the highest sensitivity point C for iron (Fe) IC, and nonferrous metal (8U
For S ), the sensitivity at point b is shown, and the phase is β (0°)
The synchronous detector 16b has the lowest sensitivity for iron (Fe), 0 point for nonferrous metal (SUS), and d point for the product (I()).

Therefore, now the iron ball is transmitting coil 12 and receiving coil 1.
3a and 13b, the output of the synchronous detector 16a whose phase is α as shown in FIG. β
The output of the synchronous detector 16b is approximately 0. In addition, in the case of a nonferrous metal ball, the synchronous detector 16a with a phase of α outputs a small detection signal gsus(α) as shown in (b) '1'', and (the phase is opposite to that of iron (Fe)). In the synchronous detector 16b whose phase is β, there is a detection signal 5US at point e.
(β) is output.

Similarly, for product (1■), as shown in (・1), the detection signal I-1 (α) at point a, which has the lowest sensitivity in the phase α synchronous detector 16a, is transferred to the β phase synchronous detector 16b. is T.I.
A detection signal (β) is output. However, in this case, as can be seen from FIG. 4, ((β)>Il, (α)).

From each of the above-mentioned plant detection signals, when a product containing iron passes through, a detection signal Fe + H (α) with a smaller amplitude than in the case of only iron balls as shown in the composite waveform (d) from 1 to 5 is obtained. However, in the metal detection device of the present invention, in the adder 20, the α-phase synchronous detector 16a has a low detection sensitivity.
6a and the signal obtained by dividing the detection signal of the β-phase synchronous detector 16b are added, so in (d), the product detection signal II(β)y! - By dividing the voltages and adding them, the detection signal 1 ((α) of the product is canceled, and as a result, the output of the adder 20 is shown in the Fe (α + β) waveform. ) will be obtained. Therefore, this signal is input to the comparator 21 and compared with the reference signal to operate the discrimination output circuit 22 to detect the presence or absence of iron.

In this way, in the case of a mixed detection signal of product and iron, the amplitude may be small or large (not shown) depending on the position of the iron ball within the product, and conventional metal detection devices cannot However, the metal detection device of the present invention takes advantage of the fact that the β phase synchronous detection output when detecting a product is in reverse phase and its amplitude is large.
Since this detection signal H (β) is divided and added to the output of the α-phase synchronous detector 16a, only the product detection signal can be canceled, and the iron detection signal F'
Only e(α) can now be detected.

No. 5 J7, Even if the foreign metal in the glass crystal is non-ferrous, i
Although detailed explanation will be omitted, the product detection signal 1
-1 (β + α) becomes zero, so only the non-ferrous detection signal is obtained (for non-ferrous metals, α phase detection level l) Since it is not large compared to the product, it will not be canceled even after being added so that it can be seen in the waveform (b) (the detection signal S
IJ S (α+β) is obtained. ).

Therefore, the partial pressure ratio of the voltage divider 23 is determined by the sensitivity of the product (such as ham or sausage) as described above.
), and the pressure is set so that (α + β) becomes zero. ,
Among the detection signals that are synchronously detected in two phases, the detection signal related to the product can be canceled by adding it in an appropriate ratio. (ferrous and non-ferrous metals) can be detected properly.

Therefore, especially if the product itself contains iron or conductive
Even in the case where the IP address is included, it has the advantage that these shadow IPs can be reduced and a more accurate detection operation can be performed.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the outline of a conventional metal detection device.
FIGS. 2(a) and 2(b) are vector diagrams showing detection operation missing explanation 1, and FIG. 3 is an embodiment 7 of the metal detection device of the present invention.
Figure 1 is a block diagram, Figure 4 is a diagram showing the relationship between the detection level and detection phase of the object to be inspected (products: ferrous and non-ferrous), and Figure 5 is a waveform diagram of the detection signal of various objects to be inspected. '. In 1, 11 is an oscillator, 12 is a sending 1g coil, and 13a1
13+) is a receiving coil, 14a and 14b are adjustment volumes, 15 is an amplifier, 16a and 16b are synchronous detectors,
17a and 17b are filters, 18a 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] AC signal - A transmitter coil excited by a bottle, a differentially connected receiver coil, two synchronous detectors that detect the output signals of the receiver coils at different phases, and two detection signals of the synchronous detectors. A metal detection device comprising: an adder that adds at an appropriate ratio; and a discrimination circuit that outputs a control signal based on the amplitude of the output signal of the adder.