JPH11258355A - Metal detection device and its adjustment method and computer readable storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detection device for easily and accurately adjusting to a phase where the influence of a body to be inspected can be minimized, its adjustment method, and a storage medium that can be read by a computer. SOLUTION: In a metal detection device with two systems of detection paths, the phase of a phase-shifting circuit according to the arctan method is calculated and set, a measurement value that is obtained when phase is shifted at each specific phase interval from the current phase is compared with the current phase at the steps (S31-S34). When the current measurement value is larger than the larger value on the first phase shifting, the minimum point of a secondary regression straight line to he cross point of two primary regression straight lines is obtained based on the measurement value that is measured until that point, and the above phase-shifting circuit is controlled so that the value is reached at the steps (S35-S38).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detecting device for detecting a metallic foreign substance mixed in a test object in a process of manufacturing foods, for example, a method of adjusting the metal detecting device, and a computer-readable storage medium. .

[0002]

2. Description of the Related Art Conventionally, for example, in a manufacturing process of food or the like, a metallic foreign substance (hereinafter, referred to as a foreign substance) mixed in a test object.
Metal detectors for detecting metal are widely used.

As a method of detecting a metal mixed in an object to be inspected by such a metal detecting device, a method utilizing a change in a magnetic field caused by the metal is generally used. Here, an outline of a metal detection method of a general metal detection device will be described.

FIG. 1 is a block diagram showing a configuration of a general metal detector. In FIG. 1, reference numeral 1 denotes an oscillation circuit that generates a predetermined AC signal. An oscillation coil 2 is connected to the oscillation circuit 1 and generates an alternating magnetic field.

[0005] Reference numerals 3a and 3b denote two receiving coils for receiving a magnetic field generated by the oscillation coil 2. The receiving coils 3a and 3b are arranged in an alternating magnetic field generated by the oscillation coil 2 so that the magnetic flux interlinks equally in an environment where there is no metal or the like that affects the distribution of the magnetic field. It is arranged in. The voltage difference between the electromotive forces induced in the receiving coil 3a and the receiving coil 3b is input to the amplifier circuit 4 as a received signal.

Next, reference numeral 4 denotes an amplifier circuit for amplifying a received signal. Reference numeral 5 denotes a synchronous detection circuit that performs synchronous detection of an output signal of the amplifier circuit 4 using a predetermined synchronous signal. 9 changes (shifts) the phase of the synchronization signal supplied to the synchronization inspection circuit 5
This is a phase shift circuit. Reference numeral 6 denotes an analog filter having the same center frequency as the output signal of the synchronous detection circuit 5 (hereinafter, referred to as a detection signal). Reference numeral 7 denotes a low-frequency amplifier circuit that amplifies the detection signal. Reference numeral 8 denotes a rectifier circuit that rectifies the analog output signal of the low-frequency amplifier circuit 7 into a determination circuit (not shown) or a signal form that is easily used in an external device or the like.

In the metal detecting device having such a configuration, when a metal (metal mixed in an object to be inspected) is passed between the oscillation coil 2 and the receiving coils 3a and 3b, two receiving signals are caused by the metal. Since the number of magnetic fluxes interlinking with the coil changes unnecessarily, a reception signal is output.

The received signal contains a detection signal modulated in accordance with the oscillation frequency of the oscillation circuit 1 (hereinafter, referred to as a modulation signal). Since the modulation signal is weak,
The signal is appropriately amplified by the amplifier circuit 4. Then, in order to extract a detection signal from the modulated signal, the synchronous detection circuit 5 performs synchronous detection at the same frequency as the oscillation frequency of the oscillation circuit 1 to demodulate the detection signal. The demodulated signal becomes only a detection signal by passing through the analog filter 6, and the detection signal is appropriately amplified by the low-frequency amplifier circuit 7.

The output signal of the low frequency amplifier 7 is
It is rectified by the rectifier circuit 8 and output to a not-shown determination circuit or the like. The determination circuit or the like determines whether or not metal has entered the test object based on the magnitude of the detection signal input from the rectifier circuit 8. Here, the magnitude of the detection signal (hereinafter, referred to as a detection voltage) is a peak value, an integral value, or the like of the detection signal.

Next, the metal detector having the above-described configuration is
For example, a case will be described in which a test object that affects a magnetic field, such as a content containing salt and / or a packaging material such as a metal film, is passed. In the following description, the inspection object includes the contents and the packaging material.

In the case of such a test object, unlike a test object such as a dried product, the test object itself affects the distribution of the surrounding magnetic field. A change in magnetic flux due to the test object is detected,
Normal metal detection becomes difficult. Therefore, in order to remove the influence of the test object and accurately detect the metal mixed into the test object, the following operation is required prior to the inspection.

FIG. 2 is a diagram for explaining a method of adjusting the influence of the test object in the conventional metal detection device. The magnitude of the influence of the test object, that is, the magnitude of the detection signal of the test object depends on the phase difference between the modulation signal and the synchronization signal.
Changes like the curve shown by the solid line.

Therefore, in a general method, prior to starting the actual operation on the inspection line, the operator uses a normal inspected object which is not mixed with metal as a sample, and uses the inspected object as a sample. It is passed through the metal detector several times until the output level of the test object becomes minimum, specifically, the display level of the display provided at the output stage of the rectifier circuit 8 becomes the minimum value. Up to the phase, first, the phase shift circuit 9 is changed by a predetermined phase step Δα.

Then, when the display level becomes the minimum value, the phase is further changed by .DELTA..beta. In smaller phase steps to drive the phase to the minimum level, that is, the phase in which the influence of the test object is minimized. .

In the above-described phase adjustment, since the phase from which the influence of the test object can be removed differs depending on the test object, the phase must be adjusted every time the test object changes. It takes time to start the actual operation.

As examples in which such adjustment work is improved, for example, JP-A-5-100047 and JP-A-7-092273 by the present inventors disclose a metal detection device and an adjustment method described below. Proposed.

FIG. 3 is a block diagram showing a configuration example of a conventional metal detection device. As shown in the figure, the basic configuration is substantially the same as the device configuration described with reference to FIG.
In order to minimize the influence of the device under test, each of the synchronous detection circuits, the analog filter, the low-frequency amplifier circuit, and the rectifier circuit is provided with two circuits. Extracts the detection signals simultaneously at two phases that differ by 90 degrees. The principle of the adjustment method for the object to be inspected by the metal detection device having such a configuration is as follows.

First, a signal vector diagram (FIG. 4) in which two synchronizing signals having phase angles different by 90 degrees are respectively set on the X axis and the Y axis.
In (a), the modulation signal S by the test object is X
It is assumed that there is a phase difference of θ degrees from the axis. This modulated signal S
The detection voltage output from the rectifier circuit 8a when the signal is synchronously detected with the X-axis synchronization signal is the X-axis component | Sc of the modulation signal S.
On the other hand, the detection voltage output from the rectifier circuit 8b when performing synchronous detection with the Y-axis synchronization signal is proportional to the Y-axis component | Ssin θ | of the modulation signal S.
By utilizing this relationship, the phase θ of the modulation signal S of the test object with respect to the X axis can be calculated by the following equation (where arctan represents the arc tangent; the same applies hereinafter).

Phase difference θ = arctan ((detection voltage on Y axis) / (detection voltage on X axis)) (1), As described above, the detection voltage synchronously detected on the X axis is | S
Since it is proportional to cos θ |, the phase difference between the X axis and the modulation signal S may be set to 90 degrees in order to minimize the influence of the test object. Therefore, in accordance with the phase θ of the modulation signal calculated by the equation (1), the phase of the phase shift circuit 9 as the first phase shift circuit is shifted from the 90 ° phase shift circuit 10 as the second phase shift circuit. By shifting the phase angle by (θ−90) degrees or (θ + 90) degrees (see FIG. 4B), the influence of the test object on the X axis can be minimized.

In the present application, the above adjustment method is referred to as a
This is called the rctan method.

[0021]

In the above-mentioned conventional example, the phase θ of the modulation signal S is calculated in principle, and the metal detection is performed based on the calculated phase θ such that the influence of the test object is minimized. The device can be adjusted. However,
Actually, the processing by the two signal systems after the synchronous detection circuits 5a and 5b causes slight differences in amplification degree and filter characteristics due to the influence of tolerances of components used in each circuit. Are the same, there is a difference in the actually output detection voltage. Therefore, it is not possible to accurately adjust the metal detection device to a state where the influence of the test object is minimal by using only this method. As a method for solving this problem, for example, Japanese Patent Application Laid-Open No. H07-092273 proposes a method of comparing the detection voltages of the first system and the second system, but a clear method is not described and specificity is not described. Lack.

Accordingly, an object of the present invention is to provide a metal detecting device capable of easily and accurately adjusting a phase at which the influence of a test object is minimized, a method of adjusting the metal detecting device, and a computer-readable storage medium. .

[0023]

To achieve the above object, a metal detecting device according to the present invention has the following configuration.

That is, two systems of synchronous detection means for demodulating a change in the magnetic field caused by the passage of the test object in the alternating magnetic field as a detection signal in accordance with two types of synchronization signals having a predetermined phase difference, Phase shifting means for shifting the phases of the two types of synchronization signals in order to reduce the influence on the alternating magnetic field due to the test object itself that does not contain metal foreign matter, and based on the magnitudes of the two types of detection signals. A synchronous detection type metal detection device for detecting a metal foreign substance contained in the test object, wherein the two systems of synchronous detection means when the test object containing no metal foreign substance passes through the alternating magnetic field. , And a predetermined analysis calculation based on the phases of the two types of synchronization signals at that time, the influence of the test object itself containing no metallic foreign matter on the alternating magnetic field is minimized. A phase calculation means for calculating a Eine,
And a control unit for finely adjusting the phases of the two types of synchronization signals by shifting the phase shift unit to the phase value calculated by the phase calculation unit.
This makes it possible to easily and accurately adjust the phase at which the influence of the object to be inspected is minimized.

Further, for example, the phase calculation means calculates a quadratic regression curve as the predetermined analysis calculation, and sets a minimum point of the calculated curve as a phase value at which the influence on the alternating magnetic field is minimized. Alternatively, two primary regression lines may be calculated, and the intersection of the calculated straight lines may be calculated as the phase value that minimizes the influence on the alternating magnetic field.

Alternatively, in order to achieve the above object, a method for adjusting a metal detector according to the present invention has the following features.

That is, two systems of synchronous detection circuits for demodulating, as detection signals, changes in the magnetic field caused by the passage of the test object in the alternating magnetic field as detection signals in accordance with two types of synchronization signals having a predetermined phase difference, A phase shift circuit that shifts the phases of the two types of synchronization signals in order to reduce the influence of the test object itself that does not include a metallic foreign substance on the alternating magnetic field, based on the magnitudes of the two types of detection signals. A method of adjusting a synchronous detection type metal detection device for detecting a metal foreign substance included in a test object, wherein the test object not including the metal foreign substance passes through the alternating magnetic field when the test object does not include the metal foreign substance. By performing a predetermined analysis calculation based on the detection signal output from the synchronous detection circuit and the phases of the two types of synchronous signals at that time, the influence of the test object itself containing no foreign metal on the alternating magnetic field is obtained. But A phase calculating step of calculating a phase value that also reduces the phase value of the two types of synchronization signals by shifting the phase of the phase shift circuit to the phase value calculated in the phase calculating step. And a step. This makes it possible to easily and accurately adjust the phase at which the influence of the object to be inspected is minimized. Further, the present invention is characterized by a computer-readable storage medium for operating a computer as a control device for realizing the above-described metal detection device.

[0028]

An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 5 is a block diagram showing a configuration of a metal detecting device as one embodiment of the present invention. In FIG. 1, reference numeral 101 denotes an oscillation circuit that generates a predetermined AC signal. An oscillation coil 102 is connected to the oscillation circuit 101 and generates an alternating magnetic field.

103a and 103b are oscillation coils 102
Are the two receiving coils that receive the magnetic field generated by. The receiving coils 103a and 103b are
2 are arranged in an alternating magnetic field, and are arranged so that magnetic fluxes interlink evenly in an environment where there is no metal or the like which affects the distribution of the magnetic field around the alternating magnetic field.
The voltage difference between the electromotive forces induced in the receiving coil 103a and the receiving coil 103b is input to the amplifier circuit 104 as a received signal.

Next, reference numeral 104 denotes an amplifier circuit for amplifying the received signal. Reference numerals 105a and 105b denote synchronous detection circuits that perform synchronous detection of an output signal of the amplifier circuit 104 using predetermined first and second synchronization signals.

Reference numeral 109 denotes a phase shift circuit that changes (shifts) the phase of the first synchronization signal supplied to the synchronization detection circuit 105a in accordance with an external setting. 110 is
According to an external setting, a phase difference of 90 degrees or a very small phase difference (for example, 0.1
(2 degrees or about 3 degrees).

The analog filters 106a and 106b have the same center frequency as the output signals (detection signals) of the synchronous detection circuits 105a and 105b. 107
a and 107b are determined according to the amplification degree set from the outside.
This is a variable amplifier circuit that amplifies the detection signal. 108a. 1
A rectifier circuit 08b rectifies the analog output voltages of the variable amplifier circuits 107a and 107b into a signal form that can be easily used in a subsequent circuit. 111a, 111b are connected to the rectifier circuits 108a. 108b analog output voltage (hereinafter, referred to as
This is an analog / digital (hereinafter, referred to as A / D) conversion circuit for converting a detection voltage into digital data.

Reference numeral 112 denotes a set value of the phase shift circuit 109, a set value of the phase difference selection circuit 110, and the A / D conversion circuits 111a, 1a representing the detected voltages.
11b is a storage unit for storing data output from 11b. An arithmetic unit 113 for analyzing the data stored in the storage unit 112 according to a predetermined method to calculate a phase value that minimizes the influence on the magnetic field of the test object (normal test object itself containing no metal). It is. Reference numeral 114 denotes a signal corresponding to the degree of amplification to the variable amplifier circuits 107a and 107b, a signal corresponding to the phase of the first synchronization signal to the phase shift circuit 109, and a phase according to the calculation result of the calculation unit 113. The phase difference selection circuit 110 is a control unit that controls the operation of the metal detection device by setting a signal corresponding to the phase difference. And
Reference numeral 115 denotes a display capable of displaying an operation state of the metal detection device by the control unit 114 and inputting various settings.

In the following description, the synchronous detection circuit 1
The path from 05a to the rectifier circuit 108a is called a first system, and the path from the synchronous detection circuit 105b to the rectifier circuit 108b is called a second system.

Next, a description will be given of a method of automatic adjustment for eliminating the influence of the test object on the magnetic field in the metal detecting device having the configuration shown in FIG. This automatic adjustment is started when the operator sets the metal detection device to the adjustment mode via the display 115, and includes four steps [Step 1] to [Step 4] described below, namely, [Step 1]. Gain adjustment, [step 2] phase calculation / setting by arctan method, [step 3] phase calculation / setting by analysis, [step 4] final gain adjustment. Hereinafter, each step will be described with reference to the flowcharts of FIGS.

The control unit 114 provides guidance to the operator in the adjustment mode from [Step 1] to [Step 1] described later so that the operator can know the progress and progress of the current adjustment on the display 115. 4], the adjustment step number, the gain during the adjustment, the phase value, and the like are appropriately displayed.

[Step 1] Gain adjustment: In this step, the variable amplifying circuit 107a and the variable amplifying circuit 107a are controlled so that the detection voltage when the test object passes through the metal detection device becomes an appropriate value.
This is the step of adjusting the gain of 107b.

First, the control unit 114 controls the phase shift circuit 1
09 is initialized to a predetermined value, and the phase difference selection circuit 110 is initialized to 90 degrees (step S11).

Next, the test object is passed through the metal detection device in the setting state of step S11, and the detection voltages of the first and second systems are measured by the A / D conversion circuits 111a and 111b. For example, if the A / D conversion circuits 111a and 111b
When converting the range of the analog input voltage of ５5 V into digital data of 0 to 255, the detection value (the detection voltage obtained by digitally converting the detection voltage is output from at least one of the two A / D conversion circuits to the control unit 114). Value) is 25
5, the control unit 114 determines that the detected voltage is A /
It is determined that the input range of the D conversion circuits 111a and 111b is exceeded, and the gain of the variable amplifier circuits 107a and 107b is controlled to be reduced. Even if the detected value is too small, A
Since the quantization error due to the / D conversion increases, for example,
When the detected value is 50 or less, control is performed so as to increase the gain. Thus, the A / D conversion circuits 111a, 111b
Is read by the control unit 114, and the gain of the variable amplifier circuit is adjusted so that the read detection value falls within a predetermined range (step S12).

When the detected voltages measured by the A / D conversion circuits 111a and 111b fall within a predetermined range (step S13), the control unit 114 proceeds to the next [step 2].

[Step 2] Calculation and setting of phase by arctan method: In this step, arc described in the prior art is used.
In this step, the phase at which the influence of the test object is minimized is calculated by the tan method, and the calculated phase is set in the phase shift circuit 109.

The detection values digitally converted by the A / D conversion circuits 111a and 111b are input to the calculation unit 113 via the storage unit 112. The calculation unit 113 calculates the modulation signal of the test object and the phase difference θ of the X-axis according to the following two equations. However, A / D repetition circuit 1
AD11a, A / D conversion circuit 111
The detected value of b is set to AD111b (step S21).

Phase difference θ = arctan ((AD111b) / (AD111a)) (2), The control unit 114 receives the phase difference θ calculated by the calculation unit 113, and according to the value, the phase shift circuit 109 Is shifted to the phase of (θ−90) degrees from the current value (step S22). Thereby, the X-axis side (the first system side) is set to a state where the influence of the test object is small. However, in this state, the influence of the test object has not been completely suppressed, so that the process proceeds to the next step and further adjustment is performed.

[Step 3] Calculation and setting of phase by analysis: In this step, the detected voltage around the phase obtained by the phase calculation in [Step 2] is measured, and the phase at which the influence of the object to be inspected is minimized is increased. Set to accuracy.

First, the control unit 114 sets the phase difference selection circuit 110 to a predetermined minute phase difference so that the first system and the second system are close to each other from the viewpoint of phase (step S31).

Next, the control unit 114 converts the detection voltages generated in the first and second systems by the operator by passing the object to be inspected through the metal detection device in the above-mentioned state into the A / D conversion circuit 111a. , 111b, and the measured values of the first and second systems and the phase values of the first and second synchronization signals are stored as a set in the storage unit 112 (step S32).

Next, the control unit 114 refers to the measured values of the first system and the second system stored in the storage unit 112 and determines the direction in which the detected values become smaller.
Then, the control unit 114 controls the phase shift circuit 109 so as to perform the first phase shift at a predetermined phase interval in a direction in which the detection value decreases (step S33).

When the first phase shift is completed, the operator passes the inspection object again, and the control unit 114
The storage unit 112 further stores a set of measured values corresponding to the detection voltages of the system and the second system, and the phase values of the first and second synchronization signals. Here, the phase value of the first synchronization signal is the set value of the phase shift circuit 108, and the phase value of the second synchronization signal is the set value of the phase shift circuit 108,
This is a value obtained by adding 10 set values.

This series of processing is repeated until the measured value corresponding to the detected voltage stored in the storage unit 112 exceeds the larger measured value stored at the time of the first phase shift (step S34). FIG. 6 shows the state of this phase shift processing.

Next, the calculation unit 113 refers to the data of the phase value and the detected value stored in the storage unit 112, and based on the data, a quadratic regression curve y = a × X ↑ 2
+ B × X + c (where m ↑ n represents m raised to the nth power,
a, b, and c represent the calculated coefficients), and calculate the minimum point (X = −b / 2a) of the curve y (step S37). This is shown in FIG.

The value of the minimum point calculated in step S37 is
This is the phase value that minimizes the influence of the test object. Therefore, the control unit 114 controls the phase shift circuit 109 so that the value (phase value) of the minimum point calculated by the calculation unit 113 is obtained (step S38).

However, depending on the object to be inspected, the above curve y
Since the slope differs between the right side (the direction in which the phase decreases) and the left side (the direction in which the phase increases) of the phase at which the detection voltage becomes the smallest, the data used for the quadratic regression curve as the number of measurements increases As the number increases, a problem may occur in the accuracy of the calculated minimum point. Therefore, it is determined whether or not the number of data, that is, the number of times of the phase shift processing has become larger than a predetermined value (step S35). If the determination is NO, the value of the minimum point is calculated based on the quadratic regression curve (step S37).

On the other hand, in step S35, YE
In the case of S, the calculation unit 113 classifies the data into a phase on the right side and a phase on the left side of the minimum phase as step S36, and based on the data on the left and right, two linear regression lines y = a1 × X + b1, y = a2 × X + b2 (where a
1, a2, b1, and b2 represent calculated coefficients), and the intersection of the two linear regression lines (X = (b1-b
2) / (a2-a1)) is determined as a phase value that minimizes the influence of the test object (see FIG. 8). Then, the control unit 114 sets a phase value in the phase shift circuit 109 according to the value of the minimum point calculated by the calculation unit 113 (step S38).

[Step 4] Final gain adjustment: After the phase of the first synchronization signal is set in step S38 of [step 3], the state is the same as when the phase was set in step S22 of [step 2]. In addition, the influence of the test object is further finely adjusted to a minimum state, and the detection voltage of the first system generated by the test object is suppressed to a very low level. Therefore, the detection value is stored in the storage unit 112 every time the object to be inspected is passed several times through the metal detection device so that the metal foreign substance can be inspected with higher sensitivity (steps S41 and S42). And
The calculation unit 113 calculates the average value and the standard deviation of the test values stored in the storage unit 112, and calculates, for example, a gain at which a value obtained by adding the average value and the standard deviation becomes a predetermined appropriate level. , Calculation unit 11
3 is set in the variable amplifier circuit 107a (step S43).

According to the adjustment steps of [Step 1] to [Step 4] described above, the operator only needs to pass the normal sample to be inspected through the metal detection device.
The metal detector can be automatically adjusted to a state where the influence of the test object is minimal. Thereby, the metal foreign matter mixed in the test object in the actual operation can be inspected with high accuracy by the metal detection device.

In the above-described embodiment, the configuration is such that the operator himself / herself passes the sample to be inspected through the metal detector in the adjustment mode. However, the present invention is not limited to this. It is needless to say that the passage itself may be automatically performed under the control of the control unit 114.

<Modification of Embodiment> As a modification of the above-described embodiment, as shown in FIG. 13, a second phase shift circuit 109b is replaced with a phase shift circuit 109a instead of the phase difference selection circuit 110 of FIG. They may be provided in parallel. In this case, the phase value of the second synchronization signal set in the second phase shift circuit 109b, that is,
The operation unit 113 calculates a phase value having a phase difference of 90 degrees or a very small value from the first synchronization signal, and the calculated value is transmitted to the second phase shift circuit 1 via the control unit 114.
09b may be set.

In the above embodiment, the storage unit 112, the arithmetic unit 113, and the control unit 11
4 are constituted by individual units, but the present invention is not limited to this. Instead of these circuits, a microcomputer in which software for realizing the operations shown in the flowcharts of FIGS. Prepared,
The operation of each unit may be realized by the microcomputer.

In this embodiment, software for realizing the operations shown in the flowcharts of FIGS.
For example, by storing the information in a storage medium such as a floppy disk and reading the information in the storage medium into, for example, a personal computer, the computer operates as the storage unit 112, the arithmetic unit 113, and the control unit 114 according to the present embodiment. Needless to say, the present invention can also be applied to the case where the user is allowed to do so.

[0061]

As described above, according to the present invention,
A metal detection device that can be easily and accurately adjusted to a phase at which the influence of a test object is minimized, a method of adjusting the metal detection device, and a computer-readable storage medium are provided. Thus, it is possible to accurately calculate and set the phase at which the influence of the test object is minimized simply by passing the test object to the metal detection device, and to adjust the metal detection device extremely easily and with high accuracy. be able to.

[0062]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a general metal detection device.

FIG. 2 is a diagram illustrating a method of adjusting the influence of a test object in a conventional metal detection device.

FIG. 3 is a block diagram illustrating a configuration example of a conventional metal detection device.

FIG. 4 is a supplementary explanatory view of an adjustment method for an object to be inspected in a conventional metal detection device.

FIG. 5 is a block diagram showing a configuration of a metal detection device as one embodiment of the present invention.

FIG. 6 is a supplementary explanatory diagram of an adjustment method for an object to be inspected as one embodiment of the present invention.

FIG. 7 is a supplementary explanatory diagram of an adjustment method for an inspection object as one embodiment of the present invention.

FIG. 8 is a supplementary explanatory diagram of an adjustment method for an object to be inspected as one embodiment of the present invention.

FIG. 9 is a flowchart illustrating an adjustment procedure of the metal detection device according to the embodiment of the present invention ([Step 1]).

FIG. 10 is a flowchart illustrating an adjustment procedure of the metal detection device according to the embodiment of the present invention ([Step 2]).

FIG. 11 is a flowchart illustrating an adjustment procedure of the metal detection device according to the embodiment of the present invention ([Step 3]).

FIG. 12 is a flowchart illustrating an adjustment procedure of the metal detection device according to the embodiment of the present invention ([Step 4]).

FIG. 13 is a block diagram illustrating a configuration of a metal detection device as a modification of one embodiment of the present invention.

[Explanation of symbols]

1, 101: oscillation circuit, 2, 102: oscillation coil, 3a, 3b, 103a, 103b: reception coil, 4.104: amplification circuit, 5, 5a, 5b, 105a, 105b: synchronous detection circuit, 6.6a, 6b, 106a, 106b: analog filter, 7, 7a. 7b: low frequency amplifier circuit, 107a, 107b: variable amplifier circuit, 8, 8a. 8b, 108a, 108b: rectifier circuit, 9, 109.109a, 109b: phase shift circuit, 10: 90 degree phase shift circuit, 110: phase difference selection circuit, 111a, 111b: A / D conversion circuit, 112: storage unit , 113: arithmetic unit, 114: control unit, 115: display,

Claims (12)

[Claims] 1. Synchronous detection means of two systems for demodulating a change in a magnetic field caused by a test object passing through an alternating magnetic field as a detection signal according to two types of synchronization signals having a predetermined phase difference, respectively. In order to reduce the influence on the alternating magnetic field due to the test object itself that does not contain metallic foreign matter,
A phase shift means for shifting the phase of the synchronization signal of the type, and a metal detection device of the synchronous detection system for detecting a metal foreign substance contained in the test object based on the magnitudes of the two types of detection signals. A predetermined object based on the detection signals from the two systems of synchronous detection means when an object to be inspected containing no metallic foreign substance passes through the alternating magnetic field and the phases of the two types of synchronous signals at that time. By performing an analysis calculation, a phase calculation unit that calculates a phase value at which the influence on the alternating magnetic field by the test object itself that does not include a metallic foreign matter is minimized, and the phase shift unit is calculated by the phase calculation unit. Control means for finely adjusting the phases of the two types of synchronization signals by shifting the phase to a phase value. 2. The phase calculation means calculates a quadratic regression curve as the predetermined analysis calculation, and calculates a minimum point of the calculated curve as a phase value at which the influence on the alternating magnetic field is minimized. The metal detector according to claim 1, wherein: 3. The phase calculation means calculates two primary regression lines as the predetermined analysis calculation, and calculates an intersection of the calculated lines as a phase value at which the influence on the alternating magnetic field is minimized. The metal detecting device according to claim 1, wherein 4. The phase calculation means calculates a quadratic regression curve as the predetermined analysis calculation, and calculates a minimum point of the calculated curve as a phase value at which the influence on the alternating magnetic field is minimized. A first phase calculating means, a second primary regression line is calculated as the predetermined analysis calculation, and an intersection of the calculated straight lines is calculated as a phase value which minimizes the influence on the alternating magnetic field. The first or second phase calculation means in accordance with the number of data representing the two detection signals and the phases of the two types of synchronization signals, which are used for calculating a phase value. 2. The metal detecting device according to claim 1, wherein the means is selectively used. 5. A phase shift circuit for shifting a reference first synchronization signal to realize the two types of synchronization signals, and the predetermined phase shift circuit according to the first synchronization signal. The metal detection device according to claim 1, further comprising: a phase difference selection circuit that generates a second synchronization signal having a phase difference of: 6. The metal detecting apparatus according to claim 1, wherein said phase shift means includes two phase shift circuits to realize said two kinds of synchronization signals. 7. The metal detecting apparatus according to claim 1, further comprising a display unit for displaying a progress of adjustment of the inspection object and a set value during the adjustment. 8. The metal detector according to claim 1, wherein the phase shifter calculates the phases of the two types of synchronization signals by an arctan method. 9. A two-system synchronous detection circuit for demodulating, as detection signals, changes in a magnetic field caused by a test object passing through an alternating magnetic field, according to two types of synchronous signals having a predetermined phase difference, In order to reduce the influence on the alternating magnetic field due to the test object itself that does not contain metallic foreign matter,
A phase shift circuit for shifting the phase of the synchronization signal of the type, and adjusting the metal detection device of the synchronous detection method for detecting a metal foreign substance contained in the test object based on the magnitudes of the two types of detection signals. A method, wherein a test object containing no metallic foreign matter passes through the alternating magnetic field, a detection signal output by the two-system synchronous detection circuit, and a phase of the two types of synchronous signals at that time. By performing a predetermined analysis calculation based on the phase calculation step of calculating the phase value that minimizes the influence on the alternating magnetic field by the test object itself that does not include metal foreign matter, A control step of finely adjusting the phases of the two types of synchronization signals by shifting the phase of the phase shift circuit to a phase value. 10. In the phase calculating step, a quadratic regression curve is calculated as the predetermined analysis calculation, and a minimum point of the calculated curve is calculated as a phase value at which the influence on the alternating magnetic field is minimized. The method for adjusting a metal detecting device according to claim 9, wherein: 11. In the phase calculating step, two primary regression lines are calculated as the predetermined analysis calculation, and an intersection of the calculated straight lines is calculated as a phase value at which the influence on the alternating magnetic field is minimized. The method for adjusting a metal detecting device according to claim 9, wherein: 12. A change in a magnetic field caused by a test object passing through an alternating magnetic field is determined by a predetermined phase difference.
Two types of synchronous detection means for demodulating the respective types of synchronous signals as detection signals, and shifting the phases of the two types of synchronous signals so as to reduce the influence on the alternating magnetic field by the test object itself which does not contain metal foreign matter. With compatible phase shift means,
A computer-readable storage medium storing a control program of a synchronous detection type metal detection device for detecting a metal foreign substance included in a test object based on the magnitudes of the two types of detection signals, the storage medium comprising: With the medium, a computer is connected to a detection signal of the two systems of synchronous detection means when an object to be inspected containing no metallic foreign substance passes through the alternating magnetic field, and a phase of the two types of synchronous signals at that time. Performing a predetermined analysis calculation based on the phase calculation means for calculating a phase value at which the influence on the alternating magnetic field by the test object itself that does not include the metallic foreign matter is minimized; and A storage medium which is operated as control means for finely adjusting the phases of the two types of synchronization signals by shifting the phase to the phase value calculated by the means.