JPH09304352A - Metal detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an automatic balancing adjustment circuit from operating when a wave detection signal supplied to a wave detection circuit is adjusted in phase, while a subject for examination is placed in an alternating magnetic field. SOLUTION: This metal detector includes a circuit 20 which excites an oscillating coil 2 by means of an ac signal to produce an alternating magnetic field, so that signals from receiving coils 3a, 3b interlined with magnetic flux are demodulated to the magnetic field, and which automatically balances steady- state signals, derived from the aged deterioration of the receiving coil 3a, 3b and the metal detecting device detects any metal in a subject W for examination, which is conveyed between the oscillating coil 2 and each receiving coil 3a, 3b. In this case, a cancel signal control circuit 21 which controls the output of a cancel signal for automatic balancing is provided inside the automatic balancing circuit 20, and while a wave detection signal supplied to a wave detection circuit 6a is being adjusted in phase, a feedback loop is opened via the cancel signal control circuit 21 by means of an automatic balance control signal output from a judging circuit 8 in the metal detecting device, so that the cancel signal is held in an uncontrolled state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detection device for detecting a metallic foreign substance mixed in an inspected object, for example, daily commodities such as food.

[0002]

2. Description of the Related Art Mainly when metal foreign substances are mixed in daily commodities such as foods, they cause great troubles in quality, especially in hygiene, and cause great damage to production materials. It can happen. Therefore, at these production sites, it is necessary to detect metals during and after production.

Conventionally, as a metal detection device for detecting the metal mixed in the inside of this type of object to be inspected, for example, there is one shown in the block diagram of FIG. That is, in the figure, 1 is an oscillator for generating an AC signal, particularly a high frequency signal, 2 is an oscillation coil connected to the oscillator 1, and 3a and 3b are oscillation coils 2 according to the AC signal from the oscillator 1. Are arranged in an alternating magnetic field generated by the receiver coil and are interlinked with the magnetic flux in the magnetic field. Normally, the voltage and the phase generated from the two receiver coils 3a and 3b are adjusted to be equal, and the differential amplifier 4a The output from is zero.

Next, in the magnetic field, the object W to be inspected is moved in the direction of the arrow by the conveying means, for example, the belt conveyor 5. When no metal is mixed in the inspected object W moving in the magnetic field, the magnetic flux does not change, and the voltages of the reception signals from the two reception coils 3a and 3b are equal,
Therefore, nothing is output from the differential amplifier 4a.

However, when metal is mixed in the object W to be inspected, the magnetic flux changes, and the two receiving coils 3a,
The voltage of the received signal from 3b will not be equal, thus
An unbalanced signal is output from the differential amplifier 4a. This unbalanced signal is a modulated signal whose oscillation frequency is modulated by a metal signal.

This modulated signal is demodulated by the first detection circuit 6a, and the switching circuits 11a and 11b described later extract only the metal detection signal through the filter circuit 7 and output it to the judgment circuit 8. When the demodulated signal exceeds the reference level set by the determination circuit 8, it is determined that the metallic foreign matter is detected. When the belt conveyor 5 is moving, the filter circuit 7 becomes a signal whose modulated signal fluctuates in proportion to the conveying speed. Therefore, normally, the filter circuit 7 is a low-pass filter having a pass frequency of about several Hz. , Bandpass filters are used.

By the way, in practice, when the object W to be inspected contains moisture or is packaged with aluminum vapor-deposited paper, aluminum foil, etc., even if no metallic foreign matter is mixed in, the influence of Since the magnetic flux in the magnetic field changes,
A change occurs in the differential amplifier 4a, and the unbalanced output by the inspection object W itself significantly reduces the sensitivity of the metal detection device. Therefore, in order to minimize the influence of the unbalanced output due to the object to be inspected W itself, the phase of the detection signal supplied to the first detection circuit 6a that demodulates the unbalanced output by the output signal from the determination circuit 8. Must be adjusted by the first phase shift circuit 9a.

Therefore, the inventors of the present application, in order to adjust the phase of the detection signal, as shown in FIG.
The first averaging circuit 10a for averaging the output from the detection circuit 6a and the switching circuits 11a and 11b that are switched by the output from the determination circuit 8 are provided, and via the switching circuits 11a and 11b, The first averaging circuit 10a is switched and connected instead of the filter circuit 7, and a conveyance control circuit 12 that controls the belt conveyor 5 according to an output signal from the determination circuit 8 is provided. .

Then, when the phase of the detection signal from the first phase shift circuit 9a is adjusted by the output signal from the determination circuit 8, the output signal from the determination circuit 8 passes through the switching circuits 11a and 11b. To the side of the first averaging circuit 10a, and the output of the first detection circuit 6a is averaged by the first averaging circuit 10a to be output. The object to be inspected W is placed in the alternating magnetic field while the belt conveyor 5 is stopped, and the phase of the detection signal supplied to the first detection circuit 6a is changed to change the first averaging circuit 10
The phase of the output of a is automatically adjusted to zero.

Next, after the phase adjustment, the first detection circuit 6a is passed through the switching circuits 11a and 11b.
The output of the above is switched to the side of the filter circuit 7 to extract a necessary signal, and the belt conveyor 5 is moved through the conveyance control circuit 12 so that the object to be inspected W is
We have already proposed a metal detection device that can determine the mixture of metals. (Japanese Patent Application No. 8-100755)

In the above-mentioned proposed metal detecting device,
When the object to be inspected W is placed in the alternating magnetic field and the output of the first detection circuit 6a is as shown in FIG. 5 (a) at a certain set value of the first phase shift circuit 9a, The average value of the areas of the output values of the first detection circuit 6a is converted to + by the first averaging circuit 10a. Further, when the set value of the first phase shift circuit 9a is changed and the output of the first detection circuit 6a is as shown in FIG. 5 (b), the average value thereof becomes-. Further, in the case as shown in FIG. 5C, the average value is zero, and the phase value of the first phase shift circuit 9a at this time is the output of the inspection object W being zero. It becomes a phase.

On the other hand, in the long term, the equilibrium state of the oscillating coil 2 and the receiving coils 3a and 3b is broken due to changes in the coil resistance values due to mechanical strain and temperature changes, and the differential amplifier 4a outputs Output is not zero, oscillator 1
A signal with the same frequency and a certain amplitude (hereinafter,
It outputs a steady signal). When this steady signal becomes large, the noise of the output signal output from the filter circuit 7 becomes large, so that the detection sensitivity decreases, and in the worst case, metal detection may become impossible.

Therefore, as shown in FIG. 4, the differential amplifier circuit 4 is provided between the differential amplifier 4a and the first detection circuit 6a.
An automatic balance adjustment circuit 20 is provided which inserts b and puts the steady signal in a balanced state. The automatic balance adjustment circuit 20 has two input terminals IN1 and IN2.
To the AC signal from the oscillator 1 and the output signal from the differential amplifier circuit 4b, respectively, and based on these signals, a cancel signal having the same frequency, the same amplitude, and the same phase as the stationary signal is output from the output terminal. Occurs at OUT. Then, by feeding back the cancel signal to the input side of the differential amplifier circuit 4b, the differential amplifier circuit 4b
The steady signal is set to zero on the output side of b, and the balance is automatically adjusted.

As the automatic balance adjustment circuit 20, the applicant of the present application generates an A / D signal to generate the cancel signal.
A circuit composed of a conversion circuit, a D / A conversion circuit, and a microcomputer for inputting and outputting data to and from them (Japanese Patent Application No. 7-725).
No. 18), and an A / D conversion circuit, a programmable gain amplifier, and a microcomputer for inputting / outputting data to / from them and computing (Japanese Patent Application No. 7-79302).
Have already been proposed.

[0015]

However, in the conventional metal detection device, the first phase shift circuit 9a is used.
When the automatic balance adjustment circuit 20 is operating during the phase adjustment of the detection signal from, the object to be inspected W in the alternating magnetic field generated by the oscillation coil 2 with the belt conveyor 5 stopped. , The automatic balance adjustment circuit 20 erroneously determines the signal from the object to be inspected W as the stationary signal, and cancels the signal having the same frequency, the same amplitude, and the same phase as the signal from the object to be inspected W. Is generated from the output terminal OUT, and the output of the differential amplifier circuit 4b is set to zero. Therefore, regardless of the phase of the detection signal, the first
There is a problem that the output of the averaging circuit 10a becomes small, the accuracy of the phase adjustment deteriorates, and in the worst case, the automatic adjustment of the phase becomes impossible.

On the other hand, the object W to be inspected is placed near the receiving coil 3a as shown in FIG. 6A, and the object W to be inspected is placed near the receiving coil 3b as shown in FIG. 6B. In this case, since the output of the differential amplifier 4a is inverted, the average value of the output of the first detection circuit 6a also has a different polarity,
In principle, it was impossible to judge which phase should be changed from the polarity of the first averaging circuit 10a.

Therefore, in order to adjust the phase where the output of the first averaging circuit 10a becomes zero, the phase is changed one by one and the output is confirmed by the judging circuit 8, and the output of the first averaging circuit 10a is changed. There has been a problem that it takes a lot of time to adjust the phase because it has to gradually approach the phase where the output becomes more zero.

The present invention has been made in view of the above points.
The purpose is to solve the above-mentioned problems and to prevent the automatic balance adjustment circuit from operating during the phase adjustment of the detection signal supplied from the phase shift circuit to the detection circuit with the DUT placed in the alternating magnetic field. It is to provide a detection device.

Another object of the present invention is, in principle, easy to determine in which direction the phase of the detection signal should be shifted when the object to be inspected is placed in an alternating magnetic field. And to provide a metal detection device in which the time required for the phase adjustment is shortened.

[0020]

The structure of the present invention for achieving the above object is as follows.

(1) An oscillator for generating an AC signal, an oscillating coil for generating an alternating magnetic field by the AC signal from the oscillator, and a conveying means for moving an object to be inspected in the magnetic field.
A receiving coil that interlinks with the magnetic flux in the magnetic field, an automatic balance adjustment circuit that outputs a cancel signal for canceling a signal that is constantly output from the receiving coil, and a signal from the receiving coil and the automatic balance. A differential amplifier circuit that amplifies the difference from the signal from the adjustment circuit, a detection circuit that demodulates the signal from the differential amplifier circuit, and the phase of the AC signal from the oscillator are adjusted to obtain the detected signal as the detected signal. A phase shift circuit that supplies the detection circuit, a filter circuit that extracts a necessary signal from the demodulated signal from the detection circuit, a determination circuit that determines the output signal from the filter circuit, and an output signal from the determination circuit. A switching circuit that is switched, an averaging circuit that is switched and connected via the switching circuit instead of the filter circuit, and that averages the output from the detection circuit; The output signal from the road, and a transport control circuit for controlling said conveying means.

Further, the cancel signal output from the automatic balance adjusting circuit is the same in frequency and amplitude as the steady signal from the receiving coil due to the AC signal from the oscillator and the signal from the differential amplifier circuit. A metal having the same phase, which is fed back to the input side of the differential amplifier circuit and automatically balanced by way of a feedback loop formed by the automatic balancing circuit, and is mixed into the object to be inspected. The metal detection device for detecting is as follows.

A cancel signal control circuit for controlling the output of the cancel signal is provided in the automatic balance adjustment circuit, and the phase of the detection signal supplied to the detection circuit is controlled by the automatic balance control signal output from the determination circuit. At the time of adjustment, it is characterized in that the feedback loop is opened and the cancel signal is brought into a non-controlled state via the cancel signal control circuit.

(2) An oscillator for generating an AC signal, an oscillating coil for generating an alternating magnetic field by the AC signal from the oscillator, and a conveying means for moving an object to be inspected in the magnetic field.
A receiving coil that interlinks with the magnetic flux in the magnetic field, an automatic balance adjustment circuit that outputs a cancel signal for canceling a signal that is constantly output from the receiving coil, and a signal from the receiving coil and the automatic balance. A differential amplifier circuit that amplifies a difference from the signal from the adjustment circuit, a first detection circuit that demodulates the signal from the differential amplifier circuit, and the phase of the AC signal from the oscillator is adjusted to detect the detected signal. A first phase shift circuit which is supplied as a signal to the first detection circuit, a filter circuit which extracts a necessary signal from a demodulated signal from the first detection circuit, and an output signal from the filter circuit is determined. A determination circuit, a switching circuit that is switched by an output signal from the determination circuit, and switching connection through the switching circuit, instead of the filter circuit, and averaging the output from the detection circuit. An averaging circuit, the output signal from the decision circuit, and a transport control circuit for controlling said conveying means.

Further, the cancel signal output from the automatic balance adjusting circuit is the same in frequency and amplitude as the steady signal from the receiving coil due to the AC signal from the oscillator and the signal from the differential amplifier circuit. , Signals of the same phase, which are fed back to the input side of the differential amplifier circuit through a feedback loop formed by the automatic balance adjustment circuit to be automatically balanced, and by an output signal from the determination circuit. When the phase of the detection signal from the first phase shift circuit is adjusted, the object to be inspected is placed in the alternating magnetic field with the transfer means stopped via the transfer control circuit, and the switching circuit In the metal detection device for detecting the metal mixed in the inspection object, which is adapted to switch the filter circuit to the averaging circuit via Ride there.

A cancel signal control circuit for controlling the output of the cancel signal is provided in the automatic balance adjustment circuit, and the phase of the detection signal supplied to the detection circuit by the automatic balance control signal output from the determination circuit. At the time of adjustment, the feedback loop is opened through the cancel signal control circuit to set the cancel signal in a non-controlled state, and further, a second detection circuit for demodulating a signal from the receiving coil; The phase of the detection signal from the oscillator is adjusted, the second phase shift circuit for supplying the detection signal to the second detection circuit and the demodulated signal from the second detection circuit are averaged, and the output thereof is obtained. A second averaging circuit that sends a signal to the determination circuit is connected, and the output signal from the determination circuit is used to output the signals from the first and second phase shift circuits. Phase of respective said detection signal, characterized in that it is adjusted to be different from each other.

Since the invention of claim 1 is configured as described above, when the phase of the detection signal supplied from the phase shift circuit to the detection circuit is adjusted while the object to be inspected is placed in the alternating magnetic field, The automatic balance adjustment circuit opens the feedback loop through the cancel signal control circuit to fix the cancel signal to the value immediately before the phase adjustment. And
The long-term unbalanced state such as mechanical strain and temperature change just before the phase adjustment is balanced, but the unbalanced component newly generated by the DUT is not adjusted. . Therefore, the signal from the object to be inspected W is not mistakenly determined as the stationary signal, the balance adjustment is not automatically performed, and the phase adjustment of the detection signal is not hindered.

Since the invention of claim 2 is constituted as described above, when the object to be inspected is placed in the alternating magnetic field, the phase of the detection signal supplied from the phase shift circuit to the detection circuit is as follows:
In principle, it is easy to determine in which direction the phase should be shifted, and the time required for the phase adjustment is greatly reduced. Therefore, the skill level of the operator becomes unnecessary.

Further, since each of the two phase shift circuits, the detection circuit and the averaging circuit is provided, two detection signals of different phases are supplied from each phase shift circuit to each detection circuit and demodulated respectively. Since it is possible to obtain the average value of the signal that is obtained and the amount of information relating to the phase setting increases, the phase adjustment can be performed in a considerably shorter time than in the case where a single phase shift circuit, a detection circuit and an averaging circuit are provided. It can be performed.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 and FIG.
FIG. 4 is a configuration block diagram showing respective embodiments of claims 1 and 2 of the metal detection device of the present invention, and FIG.
The same elements as those of 1 are denoted by the same reference numerals and the description thereof will be omitted.

[0031]

【Example】

First Embodiment In FIG. 1, an automatic balance adjustment circuit 20
The AC signal from the oscillator 1 and the output signal from the differential amplifier circuit 4b are input to the two input terminals IN1 and IN2, respectively, and a cancel signal is generated based on these signals. This cancellation signal has the same frequency, same amplitude, and same phase as the stationary signals from the receiving coils 3a, 3b, etc., and is provided in the automatic balance adjustment circuit 20 and controlled by the output of the judgment circuit 8. It is output from the output terminal OUT via the cancel signal control circuit 21 which is brought into the state or the non-controlled state (which remains fixed at the constant output value).

During the automatic balance adjustment operation, the judgment circuit 8
Output, the cancel signal path of the cancel signal control circuit 21 of the automatic balance adjustment circuit 20 is in the control state, and the cancel signal passes through the feedback loop formed by the automatic balance adjustment circuit 20 and the differential amplifier circuit 4b. It is fed back to the input side of and the balance is automatically adjusted.

When the phase of the detection signal supplied to the first detection circuit 6a is adjusted, the belt conveyor 5 is stopped and the automatic balance control circuit outputs the automatic balance control signal. The cancel signal path of the cancel signal control circuit 21 of 20 is set to a non-controlled state, the feedback loop is opened, and the feedback of the cancel signal to the differential amplifier circuit 4b is cut off. In the non-controlled state, the cancel signal output from the output terminal OUT of the automatic balance adjustment circuit 20 is fixed to a value immediately before the DUT W is placed in the alternating magnetic field, and the first detection is performed. The output value of the circuit 6a is input to the determination circuit 8 through the switching circuits 11a and 11b and the first averaging circuit 10a.

Then, the inspection object W is placed in the alternating magnetic field, and the judging circuit 8 changes the phase shift value with respect to the first phase shift circuit 9a while the belt conveyor 5 is stopped. The average value of the output from the first detection circuit 6a is read, and the phase shift value at which the output of the first averaging circuit 10a at each phase shift value is closest to zero is determined, The value is set in the first phase shift circuit 9a, and the phase adjustment is completed.

After the phase adjustment, the output from the first detection circuit 6a is input to the determination circuit 8 through the switching circuit 11a, 11b and the filter circuit 7. Then, the cancel signal path of the cancel signal control circuit 21 of the automatic balance adjustment circuit 20 is controlled by the output of the determination circuit 8, and the cancel signal is sent through the feedback loop 22 to the differential amplifier circuit 4b. Give feedback to the input side. As a result, the cancel signal output from the output terminal OUT of the automatic balance adjustment circuit 20 is made to follow the change in the steady signal from the receiving coils 3a and 3b, that is, the change in the unbalanced signal in the long term, and the belt. The conveyor 5 is operated to inspect the same type of inspected object W for the inclusion of metallic foreign matter.

As described above, the automatic balance adjustment circuit 20 does not feed back the cancel signal to the differential amplifier circuit 4b when adjusting the phase of the detection signal supplied to the first detection circuit 6a. In addition, since the cancellation signal having the same frequency, the same amplitude, and the same phase as the stationary signal is generated, the output of the differential amplifier circuit 4b is purely the signal from the inspection object W, and the accurate phase adjustment is performed. You can

(Second Embodiment) In FIG. 2, a signal output from the receiving coils 3a and 3b through the differential amplifier 4a and the differential amplifier circuit 4b is converted into a second detection circuit 6b.
Demodulates the signal, adjusts the phase of the AC signal from the oscillator 1 by the second phase shift circuit 9b, supplies the detected signal as the detection signal to the second detection circuit 6b, and outputs the signal from the second detection circuit 6b. The demodulated signal is supplied to the second averaging circuit 10b.
Thus, the output values are averaged and the average value is output to the determination circuit 8.

Then, the second phase shift circuit 9b controls the output signals from the determination circuit 8 so that the phases of the detection signals of the first and second detection circuits 6a and 6b are different from each other. It is adjusted and supplied to the first and second detection circuits 6a and 6b, respectively.

In addition to the original determination function, the determination circuit 8 here controls the phase of the detection signals of the first and second phase shift circuits 9a and 9b, and provides an output terminal of the first detection circuit 6a. The belt conveyor 5 is controlled through the control of the switching circuits 11a and 11b for switching the connection with the determination circuit 8 to either the filter circuit 7 side or the first averaging circuit 10a side and the conveyance control circuit 12. Is stopped or the operation is controlled.

The phase adjustment of the detection signal in FIG.
First, a description will be given. 3A and 3B are diagrams showing the principle of phase adjustment in FIG.

The first and second parts of this metal detecting device
Of the phase shift circuits 9a and 9b from the first and second detection circuits 6
When the phase of the detection signal supplied to each of a and 6b is adjusted, the conveyance control circuit 12 causes the belt conveyor 5 to move.
And the outputs of the first and second detection circuits 6a and 6b are input to the determination circuit 8 through the first and second averaging circuits 10a and 10b, respectively.

Then, the object to be inspected W is placed in the alternating magnetic field of the oscillating coil 2 and the switching circuits 11a and 1a.
1b is switched to the averaging circuit 10a side, and by the first phase shift circuit 9a and the second phase shift circuit 9b which outputs a detection signal whose phase is slightly delayed, the first and second detection circuits 6a , 6b, as shown in FIG. 3A, the output value of the first averaging circuit 10a connected to the output of the first detection circuit 6a is the second detection circuit. 6b
The value is closer to zero than the output value of the second averaging circuit 10b connected to the output of.

Further, the first and second detection circuits 6a, 6
When the respective outputs of b are as shown in FIG. 3B, the output value of the first averaging circuit 10a connected to the output of the first detection circuit 6a is −, and the output value of the second detection circuit 6b is −. It can be seen that the output value of the second averaging circuit 10b connected to the output of becomes +, and during this period, there is a phase value at which the output value becomes zero.

Therefore, these averaging circuits 10a, 10
From the output of b, the judgment circuit 8 can easily judge whether the phase value should be advanced, delayed, or between two phase values, and changes the phase value in the judged direction. As a result, the phase adjustment can be performed in a much shorter time than before.

Finally, the averaging circuit 10a or 10b
Among them, the phase value whose output is closest to zero is determined, the value is set in the first phase shift circuit 9a, and the phase adjustment is completed. After the phase adjustment, the switching circuit 11
a and 11b are switched to the filter circuit 7 side, the output value of the first detection circuit 6a is extracted through the filter circuit 7 as a necessary signal, and this signal is input to the determination circuit 8 and at the same time the carrier signal is transferred. The belt conveyor 5 is operated via the control circuit 12 and the automatic balance adjustment circuit 20 is set in the control state to inspect the same type of inspected object W for the inclusion of metallic foreign matter.

In this embodiment, the second phase shift circuit 9b
Although the phase of the output of the second phase shift circuit 9a is delayed from the phase of the output of the first phase shift circuit 9a, the same effect can be obtained by advancing the phase of the output of the second phase shift circuit 9b. .

In FIG. 2 showing this embodiment, from the oscillator 1,
Although an AC signal is supplied to the first and second phase shift circuits 9a and 9b, even if the output of the first phase shift circuit 9a is supplied to the input of the second phase shift circuit 9b, On the contrary, if the two outputs have different phases, the same effect can be obtained.

Next, referring to FIG. 2, the automatic balance adjustment circuit 2
In 0, an AC signal from the oscillator 1 and an output signal from the differential amplifier circuit 4b are input to its two input terminals IN1 and IN2, respectively, and a cancel signal is generated based on these signals. This cancellation signal has the same frequency, same amplitude, and same phase as the stationary signals from the receiving coils 3a, 3b, etc., and is provided in the automatic balance adjustment circuit 20 and controlled by the output of the judgment circuit 8. It is output to the output terminal OUT through the cancel signal control circuit 21 which is brought into the state or the non-controlled state (which remains fixed at the constant output value).

In the metal detection apparatus of this embodiment, during the automatic balance adjustment operation, the cancel signal path of the cancel signal control circuit 21 of the automatic balance adjustment circuit 20 becomes the control state by the output of the determination circuit 8, and the cancel signal is output. Is fed back to the input side of the differential amplifier circuit 4b through a feedback loop formed by the automatic balance adjustment circuit 20 and automatically balanced.

When adjusting the phase of the detection signal supplied to the first detection circuit 6a, the belt conveyor 5
And canceling the cancel signal path of the cancel signal control circuit 21 of the automatic balance adjusting circuit 20 by the automatic balance control signal output from the determination circuit 8 to open the feedback loop, The feedback of the cancel signal to the differential amplifier circuit 4b is cut off. In the non-controlled state, the cancel signal output from the output terminal OUT of the automatic balance control circuit 20 is fixed to a value immediately before the DUT W is placed in the alternating magnetic field, and the first detection is performed. The output value of the circuit 6a is input to the determination circuit 8 through the switching circuits 11a and 11b and the first averaging circuit 10a.
That is, in this non-controlled state, the automatic balance control circuit 20 does not follow the newly generated balance fluctuation amount due to the inspection object W.

The adjusting method at the time of adjusting the phase of the detected signal and after adjusting the phase is as described in the second embodiment. In particular, the automatic balance adjustment circuit 20 does not feed back the cancel signal to the differential amplifier circuit 4b when the phase of the detection signal supplied to the first detection circuit 6a is adjusted, and is the same as the steady signal. frequency,
Since the cancellation signals having the same amplitude and the same phase are generated, the output of the differential amplifier circuit 4b is purely the signal from the inspection object W, and the accurate phase adjustment can be performed.

Note that the technique of the present invention is not limited to the technique in the above-described embodiment, and may be implemented by means of another mode that achieves the same function, and the technique of the present invention can be variously modified within the scope of the above configuration. Can be changed or added.

[0053]

As is apparent from the above description, according to the metal detecting apparatus of the present invention, in the first aspect, the cancel signal control circuit for controlling the output of the cancel signal is provided in the automatic balance adjusting circuit. When the phase of the detection signal supplied to the detection circuit is adjusted by the automatic balance control signal output from the determination circuit, the feedback loop is opened through the cancellation signal control circuit to prevent the cancellation signal from becoming non-existent. Since the control state is set, the automatic balance adjustment circuit does not operate when the phase of the detection signal supplied from the phase shift circuit to the detection circuit is adjusted with the object to be inspected placed in the alternating magnetic field. Therefore, the phase adjustment of the detection signal can be performed accurately and stably.

According to a second aspect of the present invention, a cancel signal control circuit for controlling the output of the cancel signal is provided in the automatic balance adjustment circuit, and the detection is performed by the automatic balance control signal output from the determination circuit. When the phase of the detection signal supplied to the circuit is adjusted, the feedback loop is opened through the cancellation signal control circuit to put the cancellation signal in the non-controlled state, and further the signal from the reception coil is demodulated. Adjusting the phase of the detection signal from the second detection circuit and the oscillator,
A second phase shift circuit for supplying the detection signal to the second detection circuit and a demodulation signal from the second detection circuit are averaged, and an output signal thereof is sent to the determination circuit. The phase of the detection signal from each of the first and second phase shift circuits is adjusted so as to be different from each other by the output signal from the determination circuit, so that the phase difference between In principle, it is easy to determine which phase should be changed when the object to be inspected is changed, and the time required for the phase adjustment is greatly reduced. To be done.

Further, there is an effect that the time required for the phase adjustment can be shortened regardless of the skill of the operator.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment (first embodiment) of a metal detection device of the present invention.

FIG. 2 is a configuration block diagram showing another embodiment (second embodiment) of the metal detector of the present invention.

3 (a) and 3 (b) are diagrams showing the principle of phase adjustment of the detection signal supplied from the phase shift circuit in FIG. 2 to the detection circuit.

FIG. 4 is a block diagram showing a configuration of a conventional metal detection device.

5 (a), FIG. 5 (b) and FIG. 5 (c) are
It is a figure which shows the principle of phase adjustment of the detection signal supplied to the detection circuit from the phase shift circuit in the metal detection apparatus of FIG.

6 (a) and 6 (b) are diagrams showing problems of the phase adjustment of the metal detection device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 oscillator 2 oscillating coils 3a, 3b receiving coil 4a differential amplifier 4b differential amplifier circuit 5 belt conveyor 6a first detection circuit 6b second detection circuit 7 filter circuit 8 determination circuit 9a first phase shift circuit 9b second Phase shift circuit 10a First averaging circuit 10b Second averaging circuit 11a, 11b Switching circuit 12 Carrier control circuit 20 Automatic balance adjusting circuit 21 Cancel signal control circuit W Object to be inspected

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // G01N 33/02 G01N 33/02

Claims (2)

[Claims] 1. An oscillator for generating an AC signal, an oscillating coil for generating an alternating magnetic field by the AC signal from the oscillator, a conveying means for moving an object to be inspected in the magnetic field, and a magnetic flux and a chain in the magnetic field. Of the receiving coil, the automatic balance adjusting circuit that outputs a cancel signal for erasing the signal that is constantly output from the receiving coil, and the signal from the receiving coil and the signal from the automatic balance adjusting circuit. A differential amplifier circuit that amplifies the difference, a detection circuit that demodulates a signal from the differential amplifier circuit, and a phase shifter that adjusts the phase of the AC signal from the oscillator and supplies the detected signal as the detected signal to the detection circuit. A circuit, a filter circuit for extracting a necessary signal from the demodulated signal from the detection circuit, a determination circuit for determining an output signal from the filter circuit, and a switching by an output signal from the determination circuit A switching circuit, an averaging circuit that is switched and connected through the switching circuit instead of the filter circuit, and averages the outputs from the detection circuit, and the output signal from the determination circuit, A cancellation signal output from the automatic balance adjustment circuit, together with a carrier control circuit for controlling, is a steady signal from the receiving coil due to an AC signal from the oscillator and a signal from the differential amplifier circuit. Signals having the same frequency, the same amplitude, and the same phase, through a feedback loop formed by the automatic balance adjustment circuit,
In a metal detection device for detecting a metal mixed in the object to be inspected, which is fed back to the input side of the differential amplifier circuit and automatically balanced, in the automatic balancing circuit, an output of the cancellation signal is provided. A cancel signal control circuit for controlling is provided, and when the phase of the detection signal supplied to the detection circuit is adjusted by the automatic balance control signal output from the determination circuit, the feedback loop is opened via the cancellation signal control circuit. Then, the cancel signal is brought into a non-controlled state. 2. An oscillator for generating an alternating current signal, an oscillating coil for generating an alternating magnetic field by the alternating current signal from the oscillator, a conveying means for moving an object to be inspected in the magnetic field, and a magnetic flux and a chain in the magnetic field. Of the receiving coil, the automatic balance adjusting circuit that outputs a cancel signal for erasing the signal that is constantly output from the receiving coil, and the signal from the receiving coil and the signal from the automatic balance adjusting circuit. A differential amplifier circuit that amplifies the difference, a first detection circuit that demodulates a signal from the differential amplifier circuit, and a phase of an AC signal from the oscillator are adjusted to obtain the first detection signal as the detection signal. A first phase shift circuit supplied to the circuit, and a filter circuit for extracting a necessary signal from the demodulated signal from the first detection circuit,
A determination circuit for determining an output signal from the filter circuit,
A switching circuit that is switched by an output signal from the determination circuit, an averaging circuit that is switched and connected via the switching circuit instead of the filter circuit, and averages the output from the detection circuit; and the determination circuit. The cancel signal output from the automatic balance adjustment circuit is a signal from the oscillator and the signal from the differential amplifier circuit. The same frequency, the same amplitude, the same phase as the stationary signal from the receiving coil, through the feedback loop formed by the automatic balance adjustment circuit,
The carrier control is performed when the phase of the detection signal from the first phase shift circuit is adjusted by being fed back to the input side of the differential amplifier circuit for automatic balance adjustment, and by the output signal from the determination circuit. The inspection object is placed in the alternating magnetic field in a state where the conveying means is stopped via a circuit, and the filter circuit is switched to the averaging circuit via the switching circuit. In a metal detection device for detecting metal mixed in an object, in the automatic balance adjustment circuit, a cancel signal control circuit for controlling the output of the cancel signal is provided, and by the automatic balance control signal output from the determination circuit, When adjusting the phase of the detection signal supplied to the detection circuit, the feedback loop is opened and the cancellation is performed via the cancellation signal control circuit. Signal is brought into an uncontrolled state, and the phase of the detection signal from the oscillator is adjusted by demodulating the signal from the receiving coil, and the phase of the detection signal from the oscillator is adjusted to detect the detection signal from the second detection circuit. A second phase shift circuit supplied to the circuit is connected to a second averaging circuit that averages the demodulated signal from the second detection circuit and sends the output signal to the determination circuit. The metal detection device, wherein the phases of the detection signals from the first and second phase shift circuits are adjusted to be different from each other by an output signal from the determination circuit.