JPS6078378A - Metal detector - Google Patents

Abstract

PURPOSE:To adjust automatically phase so as to minimize material effect by providing a circuit which controls the phase adjustment in the direction where the peak value of the unbalance detection signal when an object to be inspected passes between two receiving coils and a transmission coil decreases. CONSTITUTION:An alternating magnetic field is generated from a transmission coil P by the oscillation signal of an oscillator 11. A differential voltage signal from a tuning circuit 13 is outputted when objects W to be inspected pass successively by each piece between the coil P and receiving coils S1, S2. The signal is inputted through an AC amplifier 14, a detecting circuit 16, a DC amplifier circuit 17, an AD converter 18 and a peak holding circuit 20 receiving the detection signal from an object detector 19 to a metal detecting circuit 21 which compares the signal with the reference signal from a reference setter 22 and outputs a metal detection signal when the signal exceeds the reference value. A decision circuit 23 makes relational decision of the peak value held in the circuit 20 and the stored peak value when the metal detection circuit is not inputted to said circuit. A change-over control circuit 24 controls the circuit 13 in the direction where the peak value decreases according to the decision circuit of said circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal detection device that detects metal mixed in an object to be inspected, and in particular, to an apparatus that automatically adjusts a mechanism to reduce the negative influence of the material of the object on metal detection during metal inspection. The present invention relates to a metal detection device that can be used to detect metals.

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. It includes two receiving coils s 1 '+1' s 2 arranged so that the induced voltages E1 and E2 generated by the intersecting alternating magnetic fields are equal. Transmitting coil P and receiving coil E11.8 arranged in this way
2, the object W to be inspected is transported by a transport device (not shown) at a predetermined speed from one receiving coil S1 to the other receiving coil S2. If metal is mixed into the test sample W, 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 81, the presence of iron deforms the magnetic path and S
1, the number of lines of magnetic force that intersect with the receiving coil S2 increases, and the induced voltage E1 increases, making it higher than the induced voltage E2 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 6, and electromagnetic flux is consumed as energy of the eddy currents, reducing the number of lines of magnetic force intersecting one receiving coil S1, causing the induced The voltage E1 decreases and becomes smaller than the induced voltage E2 of the other receiving coil S2. In this way, if metal is mixed in the test subject W, the induced voltages E1, K21+11:l of the first and second receiving coils S1 and S2 when passing through the detection section
A difference occurs, and the difference voltage between the two is output as an unbalanced signal to detect metal.

Therefore, such an influence on the magnetic lines of force is also caused by 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, opposite phenomena occur in the case of ferrous metals and non-ferrous metals regarding fluctuations in induced voltage, and the relationship between the phase of the alternating signal applied to the transmitting coil and the detection sensitivity is , the best detection sensitivity is achieved in different phases for iron and non-ferrous metals. For this reason, in a metal detection device, the differential voltage signal output from two receiving coils is changed by changing the phase of a reference phase signal made from an alternating signal of an oscillator that drives the transmitting coil, or by changing the phase of a reference phase signal made from an alternating signal of an oscillator that drives the transmitting coil, or by changing the phase of the tuned circuit of the receiving coil. The induced voltage signal and the reference phase signal are relatively adjusted and detected to obtain an unbalanced detection signal. Similarly, the degree of influence due to the material of the object to be inspected also differs depending on the phase, so 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 devices, while manually changing the phase of the reference phase signal or the phase of the tuning circuit, we use a good object to be inspected that does not contain any metal as a sample, and change the distance between the transmitting coil and the receiving coil. They also passed the signal through the signal, observed the output waveform of the unbalanced detection signal, and manually adjusted the phase to minimize the material effect.

However, this manual adjustment method for each type of object is not only extremely complicated and time-consuming, but also
High-precision adjustment was difficult.

The present invention corrects the above-mentioned drawbacks and provides a metal detection device that can automatically adjust the phase so that the material effect is minimized while the metal detection operation continues without requiring any manual adjustment. It is an object.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 4 is a block diagram of an embodiment of the 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 this 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.

This tuning circuit 13 is configured so that the phase of the induced voltage in the receiving coil can be changed by changing the capacitance of the capacitor with a changeover switch. This changeover switch consists of a manual switch (not shown) for coarse phase adjustment that can be manually changed for each type of object to be inspected, and a manual switch (not shown) for fine phase adjustment that can be changed by a switching control signal from a switching control circuit 24, which will be described later. automatic switch (not shown).

14 are receiving coils S1 and S output from the tuning circuit 13;
This is an AC amplification circuit that amplifies the differential voltage signal from 2. 1
5 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.

16 is a phase shift circuit 1 which transfers the differential voltage signal from the AC amplifier circuit 14.
This is a detection circuit that outputs an unbalanced detection signal by comparing it with the reference phase from 5. 17 is a DC amplifier circuit that amplifies the unbalanced detection signal from the detection circuit 16; 18 is a linear amplifier circuit 17;
This is an A/D conversion circuit that A/D converts the output signal of.

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.

20 receives a detection signal from the object detector 19 (
That is, each time the object to be inspected passes, the A/D conversion circuit 18
This is a peak hold circuit that holds the peak value of the output values. 21 compares the reference value preset in the reference value setter 22 (a predetermined value that varies depending on the type of object to be inspected) and the peak value held in the peak hold circuit 20, and if the peak value is larger than the reference value, This is a metal detection circuit that outputs a metal detection signal.

23 stores the output value of the peak hold circuit 20 when the metal detection signal is not output from the metal detection circuit 21, and stores this stored value and the peak newly held in the peak hold circuit 20 when the next object to be inspected passes. This is a judgment circuit that outputs a judgment signal to determine whether the newly held peak value is thicker or smaller than the stored value (i.e., the previous peak value) by comparing the value (when no metal detection signal is output). .

Reference numeral 2 denotes a switching control circuit that outputs a switching control signal to switch the automatic switch for fine phase adjustment of the tuning circuit 13 in a direction in which the peak value of the unbalanced detection signal decreases based on the determination signal. In other words, this switching control circuit 2 controls whether the switching control signal previously output to the tuning circuit 13 is controlled in the leading phase direction (increasing the capacitor capacity) or in the lagging phase direction (increasing the capacitor capacity). It memorizes whether the control is in the direction of decreasing the value. Then, this switching control circuit 2 outputs a switching control signal from the determination circuit 23 to the lagging phase direction when the previous control is in the leading phase direction and the previous control is in the lagging phase direction. In this case, a switching control signal in the leading phase direction is output. Further, when receiving a determination signal indicating that the subsequent peak value is smaller than the stored value, it outputs a control signal in the same direction as the previous control. That is, if the previous control was in the leading phase direction, a switching control signal to the leading phase direction is outputted, and if the previous control was in the trailing phase direction, a switching control signal to the trailing phase direction is outputted as well. (A flowchart is shown in FIG. 5.) 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. When a plurality of objects W to be inspected pass one by one between the transmitting coil P and the first and second receiving coils S1.82, a differential voltage signal is generated on the receiving coil side. This differential voltage signal is amplified by an AC amplifier circuit 14-, and its phase is compared with a reference phase from a phase shifter 15 by a detection circuit 16 to output an unbalanced detection signal. The unbalanced detection signal output from the detection circuit 16 is amplified by a DC amplifier circuit 17 and A/D converted by an A/D conversion circuit 18. Every time one inspected object W passes, the detection signal from the object detector 19 is received, and A for this one inspected object is detected.
/ The peak value of the output value of the D conversion circuit 18 is held. This peak value is compared with a reference value in the metal detection circuit 21, and if it is greater than the reference value, a metal detection signal is output.

The determination circuit 23 stores the output value of the peak hold circuit 2o when the metal detection signal is not output, and uses this stored value and a new value of the peak hold circuit 20 when the next object to be inspected passes.
It compares the held peak value with the peak value held (provided that no metal detection signal is output), and outputs a determination signal as to whether the subsequent peak value is thicker or smaller than the stored value (previous peak value).

Every time the switching control circuit 24 receives this determination signal, it sends a switching control signal to the tuning circuit 13, as shown in the flowchart of FIG. 5, to finely adjust the phase of the output signal on the receiving coil s1.82 side.

That is, when the subsequent peak value is greater than or equal to the previous peak, the switching control circuit sends a switching control signal in the opposite phase direction from the previous peak, and the subsequent peak value becomes smaller than the previous peak value. In this case, a switching control signal is sent in the same phase direction as the previous time.

If the peak value held in the peak hold circuit 20 is smaller than the reference value set in the reference value 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 value is smaller than the reference value, the peak values are sequentially compared in the judgment circuit 20, and when the peak value has increased from the previous time,
The switching control circuit 24 changes the phase in the opposite direction to that of the previous time, and when the peak value decreases, the phase is changed in the same direction as the previous time. The influence of the material of the body is always automatically adjusted in the direction of reduction each time the switching control signal is output. Therefore, if you change the type of object to be inspected, you only need to make coarse adjustments using a manual switch (not shown), and after the coarse adjustments are made, fine adjustments are automatically made during the actual detection operation to minimize material effects. It will be adjusted.

In the above embodiment, the tuning circuit 13 is controlled by the switching control signal.
Although the capacitance of the tuning capacitor is controlled to switch, the same purpose can also be achieved by outputting a switching control signal to the phase shifter 15 to change the phase of the reference phase signal.

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

Furthermore, although the previous peak value is compared in the determination circuit 23 as an example, the determination may be made every predetermined number of times or after a predetermined period of time has elapsed.

Since the present invention is configured as described above, the material effect is automatically adjusted to the minimum even when the objects to be inspected are sequentially transported and the metal detection operation is continued. Even if there is a difference, it is automatically adjusted, eliminating the need for complicated manual adjustments as in the past, and greatly improving the efficiency of metal detection operations.

[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. be. DESCRIPTION OF SYMBOLS 11... Oscillator, 12... Detection part, 13... Tuning circuit, 15... Phase shift circuit, 16... Detection circuit, 18
...A/D conversion circuit, 19...object detector,
20...Peak hold circuit, 21...Metal detection circuit, 22...Reference value setter, 23...Judgment circuit, 24...Switching control circuit. Patent applicant: Anritsu Electric Co., Ltd. Agent: Makoto Hayakawa, patent attorney

Claims (1)

[Scope of Claims] A transmitting coil that generates an alternating magnetic field; a first coil disposed opposite to the transmitting coil to receive the alternating magnetic field;
a detection unit comprising a second receiving coil; a detection circuit that compares phase fluctuations of the induced voltage with a reference phase and outputs an unbalanced detection signal; a phase adjustment circuit for relatively adjusting the phase of the reference phase and the reference phase; a peak hold circuit for holding the peak value of the unbalanced detection signal each time the object to be inspected passes; a metal detection circuit that compares an output value with a reference value and outputs a metal detection signal when the output value is greater than the reference value; and a metal detection circuit that outputs a metal detection signal when the output value is equal to or smaller than the reference value; a determination circuit that stores the stored output value and outputs a new determination signal to the peak hold circuit; It memorizes whether the control is in the delay direction, and in order to reduce the peak value, when a judgment signal indicating an output value or more is received from the judgment circuit, a switching control signal is sent to switch to a direction opposite to the previous control direction. a switching control circuit that outputs a switching control signal for switching to the same phase direction as the previous control direction to the phase adjustment circuit upon receiving a judgment signal indicating that the output value is not greater than the output value; A metal detection device characterized by reducing the influence of materials.