JPH0229997B2 - - Google Patents

Description

Detailed Description of the Invention <Industrial Field of Application of the Present Invention> The present invention relates to a metal detection device for detecting metal mixed in an object to be inspected, and particularly to a metal detection device that detects metals mixed into an object to be inspected, and particularly to a metal detection device that detects metals mixed in an object to be inspected. The present invention relates to a metal detection device that can automatically make adjustments to reduce the amount of metal damage during metal inspection.

<Prior Art> Metal detection devices used for the purpose of detecting minute metals mixed into products (for example, ham, sausage, miso, etc.) are generally based on the detection principle shown in FIG.

In Fig. 1, numeral 1 denotes a detection unit, which includes a transmitting coil P that generates an alternating magnetic field in response to an alternating signal from an oscillator, and a magnetic field line of the alternating magnetic field produced by the transmitting coil P that is located opposite to the transmitting coil P in equal amounts. fellowship,
Two receiving coils S arranged so that the induced voltages E1 and E2 caused by the alternating magnetic field are equal.
1 and S2.

Between the transmitting coil P and receiving coils S1 and S2 arranged in this way, the object W to be inspected is transferred to a transport device (not shown) at a predetermined speed from one receiving coil S1 to the other receiving coil S2. Roll and transport.

If metal is mixed into the object W to be inspected, the magnetic lines of force will change due to the metal.

That is, when the inspected object W contains iron, as shown in FIG. 2, when the inspected object W passes, for example, the receiving coil S1, the magnetic path is deformed by the presence of iron. , is larger than the induced voltage E2 of the lines of magnetic force intersecting the receiving coil S1.

When non-ferrous metals are mixed in, as shown in Figure 3, eddy currents flow in the non-ferrous metals, electromagnetic flux is consumed as energy of the eddy currents, and the lines of magnetic force that intersect one receiving coil S1 are reduced. , induced voltage E
1 decreases, and the induced voltage E2 of the other receiving coil S2
becomes smaller.

In this way, when metal is mixed in the inspected object W, a difference occurs between the induced voltages E1 and E2 of the first and second receiving coils S1 and S2 when passing through the detection section,
Metal is detected by outputting the difference voltage between the two as an unbalanced signal.

Therefore, such an influence on the magnetic lines of force also occurs due to the material of the object W to be inspected. That is, in the case of hum, for example, the moisture and salt in the object are conductive, causing changes in the magnetic lines of force, which appear as an unbalanced output. Therefore, in order to detect even trace amounts of metal with high precision, it is necessary to reduce the influence (material effect) caused by the material itself of the object to be inspected as much as possible.

However, as mentioned above, in the case of iron and non-ferrous metals, an opposite phenomenon occurs regarding fluctuations in induced voltage, and the phase of the alternating signal applied to the transmitting coil and the detection sensitivity are The relationship is that in the case of iron and non-ferrous metals, the best detection sensitivity is obtained at different phases.

For this reason, in metal detection devices, the ear voltage signals output from the two receiving coils are changed by changing the phase of a reference phase signal created from the alternating signal of the oscillator that drives the transmitting coil, or by changing the phase of the reference phase signal created from the alternating signal of the oscillator that drives the transmitting coil, or The induced voltage signal and the reference phase signal are relatively adjusted and detected to obtain an unbalanced detection signal. However, since the degree of influence due to the material of the object to be inspected similarly differs depending on the phase, it is necessary to adjust the phase to the minimum degree of influence for each type of object to be inspected.

For this reason, in conventional metal detection equipment, each time the type of object to be inspected changes, the line that continuously transports the objects to be inspected is temporarily stopped for metal detection.
While manually changing the phase of the reference phase signal or the phase of the tuning circuit, a good object to be inspected with no metal contamination is passed between the transmitting coil and the receiving coil many times as a sample. The phase was manually adjusted to minimize the output level of unbalanced signals due to the body material itself.

Further, even if the objects to be inspected are of the same type, the objects to be inspected that are sequentially conveyed along the line may gradually change to larger ones or smaller ones. Further, the amount of water or salt contained in the object to be inspected may gradually change. In these cases as well, the unbalanced output level changes depending on the material of the object to be inspected, so in these cases as well, the line has to be temporarily stopped and the phase has to be adjusted manually.

Furthermore, the unbalanced output level due to the material of the object to be inspected changes due to changes in temperature, so even in the case of temperature changes, the line has to be stopped and the phase has to be adjusted manually.

<Problems to be Solved by the Present Invention> However, there is no way to manually adjust the line by stopping the line each time the type of object to be inspected changes and passing a sample that does not contain metal over and over again. However, this method is extremely complicated and takes a lot of time, and because the line is temporarily stopped, the work efficiency of metal detection is significantly lowered, and high-precision adjustment is difficult.

In addition, as mentioned above, even if the specimen is of the same type, if the size or the amount of water or salt contained in the specimen gradually changes, or if the environmental temperature changes, the line can be stopped and manually inspected. Not only is it extremely troublesome to make adjustments, but it is also virtually impossible to constantly monitor changes in these matters and manually adjust them each time the changes occur.

The present invention solves these problems, and even if there is a change in the type of object to be inspected, a change in the size, moisture, or salinity of the same type, or a change in temperature, the line will not be stopped in any way.
The object of the present invention is to provide a metal detection device that can automatically adjust the phase so that the output level due to the material of the object to be inspected is minimized while continuing the metal detection operation without requiring manual adjustment. There is.

<Means for solving the above problems> In order to solve the above problems, the metal detection device of the present invention includes a transmitter coil that generates an alternating magnetic field, and a transmitter coil that faces the transmitter coil and receives the alternating magnetic field. a detection unit including first and second receiving coils arranged in the first and second receiving coils; , a detection circuit that compares the phase fluctuation of the induced voltage of the second receiving coil with a reference phase and outputs an unbalanced detection signal; and for reducing the influence of the material of the object to be inspected on the unbalanced detection signal. , a phase adjustment circuit for relatively adjusting the phase of the induced voltage of the receiving coil and the reference phase; and a peak hold circuit for holding the peak value of the unbalanced detection signal each time the object to be inspected passes. and a reference value setting device in which a reference value for determining the presence or absence of metal is preset; and comparing the peak output value from the peak hold circuit with the reference value, and when the peak output value is equal to or greater than the reference value. a metal presence/absence determination circuit that outputs a metal presence signal in other cases and outputs a metal no signal in all other cases; At the same time, the currently stored peak output value is compared with the peak output value stored when a metal-free signal was received last time, and if the peak output value is greater than or equal to the previously stored peak output value, a reverse direction signal is generated. output,
In other cases, a peak value comparison circuit outputs a forward direction signal; and a peak value comparison circuit that stores whether the phase control signal last outputted to the phase adjustment circuit is a phase advance direction control signal or a phase delay direction control signal; , when receiving the reverse direction signal from the peak value comparison circuit, a phase control signal in the opposite direction to the previous phase control direction, and when receiving the forward direction signal, outputting the phase control signal in the same phase direction as the previous control direction. a phase control circuit that outputs a phase control signal to the phase adjustment circuit to control the phase of the phase adjustment circuit, and when the metal non-signal from the metal presence determination circuit is output, the The present invention is characterized in that the phase of the phase adjustment circuit is controlled by a phase control circuit in a direction in which a peak output value from the peak hold circuit becomes smaller.

<Function> As described above, in the metal detection device of the present invention, each time the object to be inspected passes, the output value of the peak hold circuit is compared with a preset reference value, and the presence or absence of metal is detected by the metal presence/absence determination circuit. It is judged by.

In the case of no metal, the peak value comparison circuit stores the peak output value from the peak hold circuit based on the no metal signal from the metal presence/absence determining circuit.

The peak value comparison circuit calculates the peak output value when no metal is present (that is, the peak output value smaller than the reference value),
Compares the peak output value stored during the previous metal-free time, and outputs a reverse direction signal if it is greater than or equal to the previous stored value.
Otherwise, it outputs a forward signal.

The phase control circuit memorizes whether the phase of the phase adjustment circuit was previously controlled to be an advanced phase or a delayed phase, and when receiving the reverse direction signal, it receives a forward direction signal in the opposite direction to that of the previous time. and perform phase control in the same direction as last time.

In other words, the peak output value when there is no metal is an unbalanced output caused by the material itself of the inspected object, and if the peak output value when there is no metal is higher this time than the previous time, then Since the phase control is performed in the opposite direction to the phase control direction of , the unbalanced output due to the material of the object to be inspected is controlled in the direction of decreasing. If the current output is smaller than the previous one, phase control is performed in the previous phase control direction and in the trunk direction, so that the unbalanced output due to the material of the object to be inspected is controlled in a direction that further decreases.

Therefore, in metal detection, when metal is not included in the object to be inspected, the unbalanced output due to the material itself to be inspected is always controlled in the direction of decreasing.
Even if the type of object to be inspected changes, the size of the object to be inspected,
Even if the amount of moisture or salt changes, or the temperature changes, the line will be automatically adjusted by simply continuing to pass the test objects one after another without stopping the line.

<Embodiment of the present invention> FIG. 4 is a block diagram of an embodiment of a metal detection device according to the present invention.

In the figure, 11 is an oscillator that outputs an oscillation signal of a predetermined frequency. Reference numeral 12 denotes a transmitting coil P which is driven by the oscillation signal to generate an alternating magnetic field, and a first and second transmitting coil P which are arranged opposite to the transmitting coil P so that the lines of magnetic force of the alternating magnetic field intersect by equal amounts so that the respective induced voltages are equal. This is a detection unit including receiving coils S1 and S2.

13 is a tuning circuit for receiving coils S1 and S2.

15 is a phase shift circuit that adjusts the phase of the oscillation signal of the oscillator 11 and outputs it as a reference phase signal.

The tuning circuit 13 and the moving phase circuit 15 constitute a phase adjustment circuit 25 whose phase is adjusted by a phase control signal, which will be described later. Alternatively, the phase shifter 15 may be configured to change the phase of the reference phase signal using a phase control signal.

Reference numeral 14 denotes an AC amplifying circuit that amplifies the differential voltage signal from the receiving coils S1 and S2 outputted from the tuning circuit 13.

16 is a detection circuit that compares the differential voltage signal from the AC amplifier circuit 14 with the reference phase from the phase shift circuit 15 and outputs an unbalanced detection signal. 17 is a DC amplifier circuit that amplifies the unbalanced detection signal from the detection circuit 16.

Reference numeral 19 denotes an object detector that detects the object W to be inspected when it passes through the detection section 12 and outputs a detection signal.

Reference numeral 18 denotes a peak hold circuit that holds the peak value of the output signal of the DC amplifier circuit 17 each time it receives a detection signal from the object detector 19 (that is, each time the object to be inspected passes).

20 is an A/D conversion circuit that A/D converts the peak output value of the peak hold circuit 18.

22 is a predetermined reference value for determining the presence or absence of metal (a predetermined value that varies depending on the type of object to be inspected)
This is a reference value setter that has been set.

21 receives the peak output value from the peak hold circuit 18 via the A/D conversion circuit 20, compares it with the reference value, and outputs a metal signal when the peak output value is greater than or equal to the reference value. , otherwise it is a metal presence/absence determination circuit that outputs a metal-free signal.

23 is a first memory that newly stores the peak output value from the peak hold circuit 18 that has passed through the A/D conversion circuit 20 upon receiving the metal-free signal from the metal presence/absence determination circuit 21; When a new peak output value (i.e., the current peak output value) is stored in the storage device, the second storage device stores the storage value (i.e., the previous peak output value) that has been stored in the first storage device. The peak output values of the first and second storage devices are compared, and the current peak output value stored in the first storage device is the previous peak output value stored in the second storage device. The peak value comparison circuit includes a comparator that outputs a reverse direction signal when the output value is greater than or equal to the output value, and outputs a forward direction signal in other cases.

24 indicates whether the phase control signal previously output to the phase adjustment circuit 25 (either the tuning circuit 13 or the phase shift circuit 15) is in the leading phase direction (increasing the capacitance of the capacitor) or in the lagging phase direction. (a direction in which the capacitance of the capacitor is decreased); and upon receiving the reverse direction signal from the peak value comparison circuit 23, the information is stored in the third memory. A phase control signal in the opposite phase direction to the previous control direction is output to the phase adjustment circuit 25, and upon receiving the forward direction signal, a phase control signal in the same phase direction as the previous control direction is output to the phase adjustment circuit 25. This is a phase control circuit having a control signal output circuit. Next, the operation of the above embodiment will be explained.

First, a manual switch (not shown) for rough adjustment of the tuning circuit 13 is switched depending on the type of object to be inspected.

An oscillation signal from the oscillator 11 causes the transmitting coil P to generate an alternating magnetic field. A plurality of objects W to be inspected are sequentially connected one by one to the transmitting coil P and the first and second receiving coils S.
1 and S2, this produces a differential voltage signal on the receiving coil side. This differential voltage signal is amplified by the AC amplifier circuit 14, and its phase is changed by the phase shifter 1.
It is compared with the reference phase from 5 in a detection circuit 16 and an unbalanced detection signal is output. The unbalanced detection signal outputted from the detection circuit 16 is amplified by the DC amplifier circuit 17, and each time an object W to be inspected passes, it receives a detection signal from the object detector 19 and detects this one object W. A peak output value for the test object is held by a peak hold circuit 18, and this peak output value is A/D converted by an A/D conversion circuit 20.

Then, this A/D converted peak output value is compared with a reference value in the metal presence/absence determination circuit 21, and if it is equal to or greater than the reference value, a metal presence signal is output. In other cases, a no-metal signal indicating that no metal is included is output.

When the peak value comparison circuit 23 receives this metal-free signal, the peak value comparison circuit 23 outputs the A/D converted peak hold circuit 1.
The peak output value of No. 8 is stored in the first storage device, and the peak output value when the previous metal-free signal was received is transferred to the second storage device, and these current and previous peak output values are stored. If the current peak output value is greater than or equal to the previous one, the reverse direction signal is sent to the phase adjustment circuit 25, and if not, the forward direction signal is sent to the phase adjustment circuit 25.
(for example, the tuning circuit 13), and sends it to the receiving coil S.
1. Finely adjust the phase of the output signal on the S2 side.

That is, when the current peak output value is greater than or equal to the previous peak output value, the phase adjustment circuit 24 sends a phase control signal in the opposite phase direction to the previous one, so that the current peak output value is smaller than the previous peak output value. If so, the phase control signal is sent in the same phase direction as the previous time (as shown in the flowchart of FIG. 5).

If the peak output value held in the peak hold circuit 18 is smaller than the reference value set in the reference setter 22, no metal is mixed in the object to be inspected, and the unbalanced detection signal The output is thought to be due to the influence of the material itself of the object to be inspected on the lines of magnetic force. Therefore, when the peak output value is smaller than the reference value, the peak output value is sequentially compared by the peak value comparison circuit 22, and when the peak value has increased from the previous value, the peak output value is compared by the phase control circuit 24. The phase is changed in the opposite direction to the previous time, and if the peak value decreases, the phase is changed in the same direction as the previous time, so for each metal no-signal output, the influence of the material of the test object itself on the unbalanced detection signal output. is always automatically adjusted in the direction of reduction for each output of the phase control signal. Therefore, even if you change the type of object to be inspected, the line will not stop.
During the detection operation, it will be automatically adjusted to minimize the material effect. Additionally, it automatically follows and adjusts to changes in the size, moisture, salinity, temperature, etc. of the object to be inspected.

Further, if a signal for controlling the amplification sensitivity is sent to the DC amplifier circuit 17 based on the output signal of the peak value comparison circuit 23 for control, the amplification sensitivity can also be automatically adjusted.

In addition, the peak value comparison circuit 23 may perform the determination not every time, but every predetermined number of times, or every time a predetermined period of time has elapsed.

<Effects of the Invention> Since the present invention is configured as described above, even when the objects to be inspected are sequentially transported and the metal detection operation is continued, unbalanced output due to the material of the object to be inspected itself can be minimized. Therefore, even if you change the object to be inspected, the size of the object to be inspected, the amount of moisture or salt, or the environmental temperature changes, the system will automatically follow these changes. This eliminates the need for complicated and time-consuming adjustment work, where the line is stopped each time these changes occur and a sample that does not contain metal is passed over and over again, which requires manual adjustment. The efficiency of the process can be greatly improved, and metal detection can be performed with high precision by constantly following various changes.

[Brief explanation of drawings]

1 to 3 are diagrams showing the operating principle of the metal detection device, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. 5 is a flowchart showing the operation of essential parts of an embodiment of the present invention. It is. 11... Oscillator, 12... Detection unit, 13... Tuning circuit, 15... Phase shift circuit, 16... Detection circuit,
18...Peak hold circuit, 19...Object detection circuit, 20...A/D conversion circuit, 21...Metal presence/absence determination circuit, 22...Reference value setter, 23...Peak value comparison circuit, 24... Phase control circuit, 25...
...Phase adjustment circuit.

Claims (1)

[Scope of Claims] 1. A detection unit comprising a transmitting coil that generates an alternating magnetic field, and first and second receiving coils that are arranged to face the transmitting coil and receive the alternating magnetic field; The phase fluctuations of the induced voltages in the first and second receiving coils that occur when the object to be inspected is passed between the transmitting coil and the first and second receiving coils are compared with a reference phase to determine the difference. a detection circuit that outputs a balanced detection signal, and relatively adjusting the phase of the induced voltage of the receiving coil and the reference phase in order to reduce the influence of the material of the object to be inspected on the unbalanced detection signal. a peak hold circuit that holds the peak value of the unbalanced detection signal each time the object to be inspected passes; and a reference value setting device in which a reference value for determining the presence or absence of metal is set in advance. Compare the peak output value from the peak hold circuit with the reference value, and if the peak output value is greater than or equal to the reference value, output a signal with metal, otherwise output a signal with no metal. a metal presence/absence determination circuit that stores the peak output value from the peak hold circuit each time the metal no signal is received from the metal presence/absence determination circuit; A peak value comparison circuit that compares the peak output value stored at the time of reception and outputs a reverse direction signal if it is equal to or greater than the previously stored peak output value, and outputs a forward direction signal otherwise. and storing whether the phase control signal output last time to the phase adjustment circuit is a phase lead direction control signal or a phase delay direction control signal, and when receiving the reverse direction signal from the peak value comparison circuit. outputs to the phase adjustment circuit a phase control signal in the opposite direction to the previous phase control direction, and when receiving the forward direction signal, outputs a phase control signal in the same phase direction as the previous control direction to the phase adjustment circuit. and a phase control circuit that controls the phase of the phase adjustment circuit, and when the metal-free signal is output from the metal presence determination circuit, the phase control circuit holds the phase of the phase adjustment circuit at the peak. A metal detection device characterized in that control is performed in a direction in which a peak value output value from a circuit is reduced.