JP2021085802A - Metal foreign substance detector - Google Patents

Abstract

To provide a metal foreign substance detector that can maintain its detection accuracy even when the range of an inspection is made wider.SOLUTION: The present invention relates to metal foreign substance detectors 1, 2, and 3 having a plurality of sensor units 10 with oscillation circuits 101, 102, and 103 including a detection coil 101, the detectors outputting a detection signal of the metal foreign substance from the sensor units on the basis of the impedance change in the detection coil. When there is no impedance change in the detection coil, the oscillation circuits of the sensor units oscillate in synchronization with one another.SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal foreign matter detecting device.

Conventionally, there is a metal foreign matter detecting device that utilizes a change in oscillation frequency caused by a metallic foreign matter (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 53-195

When a plurality of metal foreign matter detection devices described in Cited Document 1 are provided to widen the inspection range, noise is generated in adjacent detection devices based on the difference in oscillation state between the detection devices, so that the detection accuracy is lowered. There is.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal foreign matter detecting apparatus in which the inspection range is widened and the detection accuracy is not easily lowered.

The mode of the metal foreign matter detection device for solving the above problems is
A metal foreign matter detection device having a plurality of sensor units having an oscillation circuit including a detection coil and outputting a metal foreign matter detection signal from the sensor unit based on impedance fluctuations of the detection coil.
When there is no impedance fluctuation of the detection coil, the oscillation circuits of the plurality of sensor units oscillate in synchronization.
It is characterized by that.

According to this metal foreign matter detecting device, the inspection range can be widened by providing a plurality of sensor units. Further, by synchronizing the oscillation states between the sensor units, it is possible to prevent the detection accuracy from being lowered.

In addition, the metal foreign matter detection device described above is
A reference oscillator that outputs a synchronization signal to the oscillation circuit of the plurality of sensor units is provided.
The oscillation circuit included in the plurality of sensor units may oscillate in synchronization with the synchronization signal.

According to this metal foreign matter detecting device, it is possible to prevent the detection accuracy from being lowered by synchronizing the oscillation state between the sensor units with the reference oscillator.

In addition, the metal foreign matter detection device described above is
The sensor unit may be formed with a PLL circuit that controls the oscillation state of the oscillation circuit so as to follow the synchronization signal of the reference oscillator.

According to this metal foreign matter detecting device, the oscillation state between the sensor units can be synchronized with the reference oscillator by the PLL circuit.

In addition, the metal foreign matter detection device described above is
The sensor unit may output a metal foreign matter detection signal using the output from the loop filter of the PLL circuit.

According to this metal foreign matter detection device, a change in the output from the loop filter when synchronizing the oscillation state of the oscillation circuit with the reference oscillator can be used as a metal foreign matter detection signal.

In addition, the metal foreign matter detection device described above is
The loop filter of the PLL circuit has a cutoff frequency lower than the frequency component of the signal input to the loop filter when the detection target passes through the detection coil.
The sensor unit may output a detection signal for a metallic foreign substance by using the output of the oscillation circuit.

According to this metal foreign matter detection device, when the detection target passes through the detection coil, the oscillation state of the oscillation circuit is not synchronized with the reference oscillator, and the change in the output of the oscillation circuit is used for the detection signal of the metal foreign matter. Can be done.

According to the above-described aspect of the metal foreign matter detecting device, it is possible to provide a metal foreign matter detecting device that has a wide inspection range but does not easily reduce the detection accuracy.

It is a block diagram which shows the structure of the metal foreign matter detection apparatus 1 of 1st Embodiment. It is a block diagram which shows the structure of the metal foreign matter detection apparatus 2 of the 2nd Embodiment. It is a block diagram which shows the structure of the metal foreign matter detection apparatus 3 of 3rd Embodiment.

[First Embodiment]
[Overview of First Embodiment (Metallic Foreign Substance Detection Device 1)]
Hereinafter, the metal foreign matter detecting device of the first embodiment will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of the metal foreign matter detecting device 1 of the first embodiment.

As shown in FIG. 1, the metal foreign matter detecting device 1 of the first embodiment includes a first sensor unit 10A, a second sensor unit 10B, and a reference oscillator 11 that sends a signal of the same frequency to these sensor units. is there. The two sensor units 10A and 10B output signals for detecting metallic foreign matter by utilizing the state change of the oscillators 102A and 102B due to the change in impedance of the detection coils 101A and 101B, and both have the same configuration. Is. In the following description, in order to distinguish which of the two sensor units 10A and 10B is configured, reference numeral A is used for the configuration of the first sensor unit 10A, and reference numeral B is used for the second sensor unit 10B. Is used. Of the two sensor units 10A and 10B, the first sensor unit 10A will be described below. Since the second sensor unit 10B has the same configuration as the first sensor unit 10A, the description thereof will be omitted.

[First sensor unit 10A (1: PLL circuit that makes the oscillation frequency follow the reference oscillator 11)]
The first sensor unit 10A has an oscillator 102A connected to a detection coil 101A and a varicap 103A, and a so-called LC oscillation circuit is formed by a combination of these. Further, in the first sensor unit 10A, a PLL circuit is formed in which the output from the oscillator 102A is made to follow the reference oscillator 11. Hereinafter, this PLL circuit will be described.

The oscillator 102A oscillates by resonance with the detection coil 101A and the capacitor in the oscillator 102A, and the capacitor component changes depending on the control voltage of the varicap 103A. A voltage controlled oscillator (VCO) is formed by a combination of these oscillators 102A, detection coil 101A, and varicap 103A.

The output from the oscillator 102A is binarized by the binarization circuit 104A, further passed through the frequency divider 105A, divided (1 / N), and then input to the phase comparator 106A. In addition to the signal from the frequency divider 105A, a signal obtained by dividing (1 / M) the signal from the reference oscillator 11 by the frequency divider 107A is input to the phase comparator 106A, and the phase difference between these signals is changed. The corresponding signal is output. The output from the phase comparator 106A passes through the loop filter 108A and becomes the control voltage of the varicap 103A. The loop filter 108A is designed so that the cutoff frequency is higher than the frequency of the signal output from the phase comparator 106A when the metal foreign matter passes through.

In the above PLL circuit, the output from the oscillator 102A follows the signal from the reference oscillator 11, and its frequency is controlled to be N / M times the oscillation frequency of the reference oscillator 11. Here, when a metal foreign object passes near or inside the detection coil 101A, the impedance (inductivity and parasitic capacitance) of the detection coil 101A changes, and the oscillation state (oscillation frequency, oscillation gain) of the oscillator 102A changes. A phase difference occurs between the signal from the oscillator 105A and the signal from the oscillator 107A. The signal corresponding to this phase difference passes from the phase comparator 106A through the loop filter 108A and is fed back to the varactor 103A as a control voltage, and the signal from the oscillator 102A is controlled to follow the signal from the reference oscillator 11 ( The oscillation frequency of the oscillator 102A becomes N / M times the oscillation frequency of the reference oscillator 11). On the other hand, the oscillation gain of the oscillator 102A becomes different from the oscillation gain in the state where there is no metal foreign matter due to the change in the impedance of the detection coil 101A and the change in the control voltage of the varicap 103A.

[First sensor unit 10A (2: circuit that outputs a detection signal for metallic foreign matter)]
Next, the circuit that outputs the detection signal of the metallic foreign matter in the first sensor unit 10A will be described.

In the first sensor unit 10A, the oscillation gain of the oscillator 102A changes as the metal foreign matter passes near or inside the detection coil 101A. The first sensor unit 10A outputs a signal for detecting a metallic foreign matter by using a change in the oscillation gain of the oscillator 102A.

First, the output from the oscillator 102A is processed by the envelope detector 111A. In the envelope detection in the envelope detector 111A, a component of the oscillation frequency of the oscillator 102A may be included, so that the filter 112A for removing the component is passed through. The frequency of the oscillator 102A is usually several hundred kHz or higher, whereas the signal component when detecting a metallic foreign substance is several tens to several hundred Hz, and the frequency gap is large. Therefore, the filter 112A is simple. It can be configured.

The signal obtained after passing through the filter 112A is amplified by the amplifier 113A to a level that is easy to handle, and further passed through the filter 114A to remove frequencies that are not involved in the detection of metallic foreign matter. In order to determine whether the signal thus obtained is a signal in which a metallic foreign substance is detected or is due to noise, the magnitude is compared with the threshold value set as the output level at the time of detecting the foreign substance in the comparator 115A. To. If the signal that has passed through the filter 114A exceeds (or falls below) this threshold value, a signal indicating that a metallic foreign matter has been detected is output, and if it does not exceed (or does not fall below) the threshold value, the metallic foreign matter is output. No signal is output indicating that is detected.

[Effects and other configurations of metal foreign matter detection device 1]
The metal foreign matter detecting device 1 of the first embodiment has two sensor units 10A and 10B, and can inspect a wider range as compared with the case where the sensor unit is one.

Further, in the metal foreign matter detecting device 1 of the first embodiment, the oscillators 102A and 102B of the two sensor units 10A and 10B both oscillate following the reference oscillator 11 regardless of the presence or absence of the influence of the metallic foreign matter, and the sensor. Oscillation synchronizes between the parts. If a plurality of sensor units are provided without using a configuration in which oscillations are synchronized between the sensor units, the oscillation frequencies and phases will be different between the sensor units, and beat noise will be generated due to this, resulting in a sensor. May be erroneously detected. In the first embodiment, since the oscillations are synchronized between the sensor units, it is possible to prevent noise caused by different oscillation frequencies and phases.

Further, in the first embodiment, a configuration is adopted in which the oscillation circuits of the first sensor unit 10A and the second sensor unit 10B are oscillated in synchronization with the signal from the reference oscillator 11, but the oscillations are synchronized between the sensor units. The configuration is not limited to this configuration, and for example, the oscillator 102B of the second sensor unit 10B can be replaced with the oscillator 102A of the first sensor unit 10A without using an external oscillator such as the reference oscillator 11. It may be configured to synchronize with the oscillation output. As a specific configuration, the reference oscillator 11 is deleted in the metal foreign matter detection device 1, and the binarization circuit 104A to the loop filter 108A of the first sensor unit 10A are deleted so that the oscillator 102A oscillates independently. Then, the output from the oscillator 102A is input to the frequency divider 107B of the second sensor unit 10B.

In adopting a configuration in which oscillations are synchronized between the sensor units, the number of sensor units is not limited to the number of sensor units of the metal foreign matter detection device 1 of the first embodiment, and for example, there are three or more sensor units. It may be.

[Second Embodiment]
[Outline of the second embodiment (metal foreign matter detection device 2)]
Hereinafter, the metal foreign matter detecting device of the second embodiment will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the metal foreign matter detecting device 2 of the second embodiment. The same reference numerals are used for the configurations common to the metal foreign matter detecting device 1 of the first embodiment.

As shown in FIG. 2, the metal foreign matter detecting device 2 of the second embodiment includes a first sensor unit 20A, a second sensor unit 20B, and a reference oscillator 11 that sends a signal of the same frequency to these sensor units. is there. The two sensor units 20A and 20B output signals for detecting metallic foreign matter by utilizing the state change of the oscillators 102A and 102B due to the change in impedance of the detection coils 101A and 101B, and both have the same configuration. Is. In the following description, in order to distinguish which of the two sensor units 20A and 20B is configured, reference numeral A is used for the configuration of the first sensor unit 20A, and reference numeral B is used for the second sensor unit 20B. Is used. Of the two sensor units 20A and 20B, the first sensor unit 20A will be described below. Since the second sensor unit 20B has the same configuration as the first sensor unit 20A, the description thereof will be omitted.

[First sensor unit 20A (1: PLL circuit that makes the oscillation frequency follow the reference oscillator 11)]
The first sensor unit 20A has the detection coil 101A and the oscillator 102A connected to the varicap 103A as in the first embodiment, and a so-called LC oscillation circuit is formed by a combination of these. Further, in the first sensor unit 20A, a PLL circuit is formed in which the output from the oscillator 102A is made to follow the reference oscillator 11. Since this PLL circuit has the same configuration as that of the first embodiment, the description thereof will be omitted.

[First sensor unit 20A (2: circuit that outputs a detection signal for metallic foreign matter)]
Next, the circuit that outputs the detection signal of the metallic foreign matter in the first sensor unit 20A will be described.

In the first sensor unit 20A, the control voltage of the varicap 103A changes as the metal foreign matter passes near or inside the detection coil 101A. The first sensor unit 20A outputs a signal for detecting a metallic foreign matter by using a change in the control voltage (output of the loop filter 108A) of the varicap 103A.

First, since the output from the loop filter 108A may include a component of the oscillation frequency of the oscillator 102A, the filter 201A for removing this component is passed through. The frequency of the oscillator 102A is usually several hundred kHz or higher, whereas the signal component when detecting a metallic foreign substance is several tens to several hundred Hz, and the frequency gap is large. Therefore, the filter 201A is simple. It can be configured.

The signal obtained after passing through the filter 201A is amplified by the amplifier 202A to a level that is easy to handle, and further passed through the filter 203A to remove frequencies that are not involved in the detection of metallic foreign matter. In order to determine whether the signal thus obtained is a signal in which a metallic foreign substance is detected or is due to noise, the magnitude is compared with the threshold value set as the output level at the time of detecting the foreign substance in the comparator 204A. To. If the signal that has passed through the filter 203A exceeds (or falls below) this threshold value, a signal indicating that a metallic foreign matter has been detected is output, and if it does not exceed (or does not fall below) the threshold value, the metallic foreign matter is output. No signal is output indicating that is detected.

[Effects and other configurations of metal foreign matter detection device 2]
The metal foreign matter detecting device 2 of the second embodiment has two sensor units 20A and 20B, and can inspect a wider range as compared with the case where the sensor unit is one.

Further, in the metal foreign matter detecting device 2 of the second embodiment, the oscillators 102A and 102B of the two sensor units 20A and 20B both oscillate following the reference oscillator 11 regardless of the presence or absence of the influence of the metallic foreign matter, and the sensor. Oscillation synchronizes between the parts. If a plurality of sensor units are provided without using a configuration in which oscillations are synchronized between the sensor units, the oscillation frequencies and phases will be different between the sensor units, and beat noise will be generated due to this, resulting in a sensor. May be erroneously detected. In the second embodiment, since the oscillations are synchronized between the sensor units, it is possible to prevent noise caused by different oscillation frequencies and phases.

In adopting a configuration in which oscillations are synchronized between the sensor units, the number of sensor units is not limited to the number of sensor units of the metal foreign matter detection device 2 of the first embodiment, and for example, there are three or more sensor units. It may be.

[Third Embodiment]
[Outline of Third Embodiment (Metallic Foreign Substance Detection Device 3)]
Hereinafter, the metal foreign matter detecting device of the third embodiment will be described with reference to the drawings. FIG. 3 is a block diagram showing the configuration of the metal foreign matter detecting device 3 of the third embodiment. The same reference numerals are used for the configurations common to the metal foreign matter detecting device 1 of the first embodiment.

As shown in FIG. 3, the metal foreign matter detecting device 3 of the third embodiment includes a first sensor unit 30A, a second sensor unit 30B, and a reference oscillator 11 that sends a signal of the same frequency to these sensor units. is there. The two sensor units 30A and 30B output signals for detecting metallic foreign matter by utilizing the state change of the oscillators 102A and 102B due to the change in impedance of the detection coils 101A and 101B, and both have the same configuration. Is. In the following description, in order to distinguish which of the two sensor units 30A and 30B is configured, reference numeral A is used for the configuration of the first sensor unit 30A, and reference numeral B is used for the second sensor unit 30B. Is used. Of the two sensor units 30A and 30B, the first sensor unit 30A will be described below. Since the second sensor unit 30B has the same configuration as the first sensor unit 30A, the description thereof will be omitted.

[First sensor unit 30A (1: PLL circuit that does not make the oscillation frequency when passing metal foreign matter follow the reference oscillator 11)]
The first sensor unit 30A has an oscillator 102A connected to the detection coil 101A and the varicap 103A, and a so-called LC oscillation circuit is formed by a combination of these as in the first embodiment. Further, in the first sensor unit 30A, a PLL circuit is formed in which the output from the oscillator 102A is made to follow the reference oscillator 11. In this PLL circuit, the cutoff frequency of the loop filter 108A is different from that of the first embodiment, so that the output from the oscillator 102A does not follow (or becomes difficult to follow) the reference oscillator 11 when a metal foreign object passes through. It is configured as follows. Hereinafter, this PLL circuit will be described.

The oscillator 102A oscillates by resonance with the detection coil 101A and the capacitor in the oscillator 102A, and the capacitor component changes depending on the control voltage of the varicap 103A. A voltage controlled oscillator (VCO) is formed by a combination of these oscillators 102A, detection coil 101A, and varicap 103A.

The output from the oscillator 102A is binarized by the binarization circuit 104A, further passed through the frequency divider 105A, divided (1 / N), and then input to the phase comparator 106A. In addition to the signal from the frequency divider 105A, a signal obtained by dividing (1 / M) the signal from the reference oscillator 11 by the frequency divider 107A is input to the phase comparator 106A, and the phase difference between these signals is changed. The corresponding signal is output. The output from the phase comparator 106A passes through the loop filter 108A and becomes the control voltage of the varicap 103A. The loop filter 108A is designed so that the cutoff frequency is lower than the frequency component (for example, 10 to 150 Hz) of the signal output from the phase comparator 106A when the metal foreign matter passes through (for example, 1 Hz). Further, the oscillation frequency of the LC circuit and the reference oscillator 11 are designed so that the frequency component of the signal output from the phase comparator 106A in the absence of metal foreign matter is lower than the cutoff frequency of the loop filter 108A. As an example, it is designed so that 1 / N of the oscillation frequency of the LC circuit and 1 / M of the oscillation frequency of the reference oscillator 11 are equal to each other.

In the above PLL circuit, in the absence of metal foreign matter, the output from the oscillator 102A follows the signal from the reference oscillator 11, and its frequency is controlled to be N / M times the oscillation frequency of the reference oscillator 11. .. Here, when a metal foreign object passes near or inside the detection coil 101A, the impedance (inductivity and parasitic capacitance) of the detection coil 101A changes, and the oscillation state (oscillation frequency, oscillation gain) of the oscillator 102A changes. A phase difference occurs between the signal from the oscillator 105A and the signal from the oscillator 107A. However, although the signal corresponding to this phase difference is output from the phase comparator 106A to the loop filter 108A, the cutoff frequency of the loop filter 108A is lower than the frequency of the signal output from the phase comparator 106A when the metal foreign matter passes through. , It is not fed back as the control voltage of the varactor 103A. As a result, the signal from the oscillator 102A is not controlled to follow the signal from the reference oscillator 11, and the oscillation state remains changed.

[First sensor unit 30A (2: circuit that outputs a detection signal for metallic foreign matter)]
Next, the circuit that outputs the detection signal of the metallic foreign matter in the first sensor unit 30A will be described.

In the first sensor unit 30A, the oscillation state of the oscillator 102A changes as the metal foreign matter passes near or inside the detection coil 101A. The first sensor unit 30A outputs a signal for detecting a metallic foreign matter by using a change in the oscillation state of the oscillator 102A.

First, the output from the oscillator 102A is input to the phase detector 301A and multiplied by the output from the reference oscillator 11. The output from the phase detector 301A is amplified to a level that is easy to handle by the amplifier 302A, and is further passed through the filter 303A to remove frequencies that are not involved in the detection of metallic foreign matter. In order to determine whether the signal thus obtained is a signal in which a metallic foreign substance is detected or is due to noise, the magnitude is compared with the threshold value set as the output level at the time of detecting the foreign substance in the comparator 304A. To. If the signal that has passed through the filter 303A exceeds (or falls below) this threshold value, a signal indicating that a metallic foreign matter has been detected is output, and if it does not exceed (or does not fall below) the threshold value, the metallic foreign matter is output. No signal is output indicating that is detected.

[Effects and other configurations of metal foreign matter detection device 3]
The metal foreign matter detecting device 3 of the third embodiment has two sensor units 30A and 30B, and can inspect a wider range as compared with the case where the sensor unit is one.

Further, in the metal foreign matter detecting device 3 of the third embodiment, in the state where there is no metal foreign matter, the oscillators 102A and 102B of the two sensor units 30A and 30B both oscillate following the reference oscillator 11, and the sensor units oscillate with each other. Oscillation synchronizes. If a plurality of sensor units are provided without using a configuration in which oscillations are synchronized between the sensor units, the oscillation frequencies and phases will be different between the sensor units, and beat noise will be generated due to this, resulting in a sensor. May be erroneously detected. In the third embodiment, since the oscillations are synchronized between the sensor units in the absence of metal foreign matter, it is possible to prevent noise caused by different oscillation frequencies and phases.

In the third embodiment, the output of the oscillator 102A and the output of the reference oscillator 11 are input to the phase detector 301A, but this configuration is used to obtain the output according to the change in the oscillation state of the oscillator 102A. The configuration is not limited to, and for example, an FM detection circuit (FV converter) may be used.

In adopting a configuration in which oscillations are synchronized between the sensor units, the number of sensor units is not limited to the number of sensor units of the metal foreign matter detection device 3 of the first embodiment, and for example, there are three or more sensor units. It may be.

[Other]
The configurations of the metal foreign matter detection devices 1 to 3 described above may be appropriately changed depending on the usage conditions and the like. For example, circuits such as a frequency divider and a filter may be added (or deleted) as appropriate. May be good. Further, in the above example, the numerical values of the division ratios M and N are not limited to specific numerical values.

Hereinafter, the configuration of the invention described above will be described. The configuration of the above embodiment corresponding to the configuration of the invention is described in parentheses.

In the above explanation,
A plurality of sensor units (for example, first sensor units 10A, 20A, etc.) having an oscillation circuit (for example, an LC oscillation circuit including oscillators 102A, 102B, varactors 103A, 103B) including detection coils (for example, detection coils 101A, 101B). 30A, second sensor units 10B, 20B, 30B), and a metal foreign matter detection device (for example, metal foreign matter detection devices 1, 2) that outputs a metal foreign matter detection signal from the sensor unit based on the impedance fluctuation of the detection coil. 3)
When there is no impedance fluctuation of the detection coil, the oscillation circuits of the plurality of sensor units oscillate in synchronization (for example, the reference oscillator 11 in the metal foreign matter detection devices 1 and 2 (in the modified example, the oscillation circuit of one of the sensor units). The oscillation circuit of the other sensor unit follows) and oscillates, and the metal foreign matter detection device 3 oscillates following the reference oscillator 11 in the absence of metal foreign matter).
A metal foreign matter detection device, characterized by the above, is described.

Further, the above-described metal foreign matter detection device.
A reference oscillator (for example, a reference oscillator 11) that outputs a synchronization signal to an oscillation circuit included in the plurality of sensor units is provided.
The oscillation circuit included in the plurality of sensor units oscillates in synchronization with the synchronization signal.
A metal foreign matter detection device, characterized by the above, is described.

Further, the above-described metal foreign matter detection device.
The sensor unit is formed with a PLL circuit that controls the oscillation state of the oscillation circuit so as to follow the synchronization signal of the reference oscillator.
A metal foreign matter detection device (see each embodiment), characterized by the above, is described.

Further, the above-described metal foreign matter detection device.
The sensor unit outputs a detection signal for a metallic foreign substance by using the output from the loop filter of the PLL circuit.
A metal foreign matter detecting device (for example, a metal foreign matter detecting device 2), characterized by the above, is described.

Further, the above-described metal foreign matter detection device.
The loop filter of the PLL circuit has a cutoff frequency lower than the frequency component of the signal input to the loop filter when the detection target passes through the detection coil.
The sensor unit outputs a detection signal for a metallic foreign substance using the output of the oscillation circuit.
A metal foreign matter detecting device (for example, a metal foreign matter detecting device 3), characterized by the above, is described.

1,2,3 Metal foreign matter detection device 10A, 20A, 30A First sensor unit 10B, 20B, 30B Second sensor unit 11 Reference oscillator 101A, 101B Detection coil 102A, 102B Oscillator 103A, 103B Barractor 104A, 104B Binarization circuit 105A, 105B Divider 106A, 106B Phase comparator 107A, 107B Divider 108A, 108B Loop filter 111A, 111B Envelope detector 112A, 112B, 114A, 114B Filter 113A, 113B Amplifier 115A, 115B Comparator 201A, 201B , 203A, 203B Filter 202A, 202B Amplifier 204A, 204B Comparator 301A, 301B Phase detector 302A, 302B Amplifier 303A, 303B Filter 304A, 304B Comparator

Claims (5)

A metal foreign matter detection device having a plurality of sensor units having an oscillation circuit including a detection coil and outputting a metal foreign matter detection signal from the sensor unit based on impedance fluctuations of the detection coil.
When there is no impedance fluctuation of the detection coil, the oscillation circuits of the plurality of sensor units oscillate in synchronization.
A metal foreign matter detection device characterized by this. The metal foreign matter detecting device according to claim 1.
A reference oscillator that outputs a synchronization signal to the oscillation circuit of the plurality of sensor units is provided.
The oscillation circuit included in the plurality of sensor units oscillates in synchronization with the synchronization signal.
A metal foreign matter detection device characterized by this. The metal foreign matter detecting device according to claim 2.
The sensor unit is formed with a PLL circuit that controls the oscillation state of the oscillation circuit so as to follow the synchronization signal of the reference oscillator.
A metal foreign matter detection device characterized by this. The metal foreign matter detecting device according to claim 3.
The sensor unit outputs a detection signal for a metallic foreign substance by using the output from the loop filter of the PLL circuit.
A metal foreign matter detection device characterized by this. The metal foreign matter detecting device according to claim 3.
The loop filter of the PLL circuit has a cutoff frequency lower than the frequency component of the signal input to the loop filter when the detection target passes through the detection coil.
The sensor unit outputs a detection signal for a metallic foreign substance using the output of the oscillation circuit.
A metal foreign matter detection device characterized by this.

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