JP2018141722A - Eddy current type metal sensor and eddy current detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current type metal sensor capable of accurately detecting an eddy current of a detected object composed of metal even with a compact and simple configuration, and highly precisely performing detection of presence/absence of metal and measurement of a distance to the metal, and an eddy current detection method capable of accurately detecting the eddy currents of the detected object composed of the metal.SOLUTION: An eddy current type metal sensor comprises: a first coil 1; a second coil 2; a first oscillation circuit 6 which oscillates including the first coil 1; a second oscillation circuit 7 which oscillates including the second coil 2; a fifth terminal of a microcomputer U1 which receives a reference time signal indicating time from an external device; a measurement part 41 which measures an oscillation frequency in each of the first oscillation circuit 6 and the second oscillation circuit 7 on the basis of the reference time signal; a calculation part 42 which calculates a difference in the oscillation frequency measured by the measurement part 41; and a conversion part 43 which converts the difference calculated by the calculation part 42 as a variation of an eddy current.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an eddy current type metal sensor and an eddy current detection method for detecting an eddy current of a detection object made of metal.

  There has been proposed an apparatus for performing various detection / detection processes on a detection object made of metal using an eddy current generated in the detection object (Patent Documents 1-3).

  Patent Document 1 includes an eddy current type sensor that detects the passage of a protrusion that rotates integrally with a rotating body, and an apparatus that detects the number of rotations of the rotating body based on a change in the magnetic field generated by the sensor coil. It is disclosed. Patent Document 2 discloses an eddy current type displacement sensor that detects the presence or absence of metal from a change in impedance of a coil caused by an eddy current generated in an adjacent metal by passing a high-frequency current through the coil. Patent Document 3 discloses an apparatus for detecting a metal mixed as a foreign material in a friction material using an eddy current sensor.

JP 2006-8929 A JP-A-8-271204 JP 2014-130075 A

  In the eddy current sensor, when the coil is used alone, there is a problem that the detection accuracy of the eddy current is lowered, and there is a problem that the detection result varies greatly due to the external environment such as temperature. In addition, since an accurate eddy current cannot be detected, metal detection based on the detected eddy current cannot be performed with high accuracy.

  Further, in the conventional eddy current type sensor, the eddy current is detected based on the clock signal of the oscillator built in the microcomputer used.

  On the other hand, in order to avoid the so-called EMI (radiated noise) problem, the clock is generally subjected to spread spectrum that intentionally changes the frequency randomly. Furthermore, the clock signal has a low frequency fluctuation (jitter) and the frequency fluctuates slightly. Therefore, the conventional eddy current type sensor has a problem that an accurate eddy current cannot be detected and an error occurs.

  There is also a method in which a dedicated oscillator (oscillator) is provided outside and the clock signal generated by the oscillator is used as a reference. However, since the oscillator is expensive, the manufacturing cost of the product is increased and the structure of the product is increased. There is a problem of making it complicated.

  The present invention has been made in view of such circumstances, and can detect an eddy current of a metal detection object more accurately without being affected by the external environment even in a small and simple configuration. Vortices that can detect the presence or absence of metal, measure the distance to metal, etc. with high accuracy, and can easily adjust the detection sensitivity of the presence or absence of the detection object or the measurement sensitivity of the distance to the detection object. An object is to provide a current-type metal sensor and an eddy current detection method.

  An eddy current type metal sensor according to the present invention includes a first oscillation circuit that oscillates including a first coil and a second coil in an eddy current type metal sensor that detects an eddy current of a detection object made of metal. A second oscillation circuit that oscillates, a reception unit that receives a reference time signal representing time from an external device, and a measurement unit that measures an oscillation frequency in each of the first oscillation circuit and the second oscillation circuit based on the reference time signal And a calculation unit that calculates a difference between the oscillation frequencies measured by the measurement unit, and a conversion unit that converts the difference calculated by the calculation unit as an amount of change in eddy current of the detected object. And

  In the eddy current type metal sensor according to the present invention, the oscillation frequency of the first oscillation circuit including the first coil disposed in the vicinity of the detected object, and the first coil in the vicinity of the detected object to the detected object. The measurement unit measures the oscillation frequency of the second oscillation circuit including the second coil arranged with different distances. At this time, the measurement unit measures the oscillation frequency based on the reference time signal received by the reception unit that receives the reference time signal from the external device. The calculation unit calculates the difference between the two oscillation frequencies measured by the measurement unit, and the conversion unit converts the difference calculated by the calculation unit as the amount of change in the eddy current of the detected object. When the eddy current of the object to be detected increases, the inductance of the coil decreases, and the oscillation frequency of the oscillation circuit including the coil increases. Here, since the amount of change in inductance corresponding to the change in eddy current increases in the coil closer to the object to be detected, fluctuations in the oscillation frequency in the oscillation circuit also increase. Therefore, the eddy current can be detected from the difference between the oscillation frequencies of the respective oscillation circuits using two coils arranged at different distances from the object to be detected. Further, based on the detected eddy current, it is possible to detect the presence or absence of the detection object, measure the distance to the detection object, and the like.

  At this time, a flat coil such as a coil formed by patterning printing on the substrate can be used as the two coils, and the configuration is downsized. In the case of a coil having a small inductance such as a flat coil, the oscillation frequency is high. As a result, since the computer clock is lower than the oscillation frequency, in the case of frequency measurement, the measurement time for obtaining the same resolution can be shortened, and the measurement time can be made constant.

  In addition, a series of processing of oscillation frequency measurement, oscillation frequency difference calculation, and conversion from difference to eddy current can be performed by software using a microcomputer, etc., and the number of parts can be reduced. The detection accuracy is high.

  The eddy current type metal sensor according to the present invention is characterized in that the measurement unit is configured to alternately measure an oscillation frequency in the first oscillation circuit and an oscillation frequency in the second oscillation circuit. To do.

  In the eddy current type metal sensor of the present invention, measurement of the oscillation frequency in the first oscillation circuit and measurement of the oscillation frequency in the second oscillation circuit are alternately performed while switching. Therefore, when the oscillation frequency of one oscillation circuit is measured, the other oscillation circuit is not oscillating. Therefore, the measurement value of the oscillation frequency of one oscillation circuit is not affected by the oscillation of the other oscillation circuit. Therefore, accurate oscillation frequencies in both oscillation circuits can be measured, and the eddy current detection accuracy is high.

  The eddy current type metal sensor according to the present invention is characterized in that the first coil and the second coil are arranged coaxially.

  In the eddy current type metal sensor of the present invention, the first coil and the second coil are arranged coaxially. Therefore, the area required for arranging the coils is small, and the eddy current type metal sensor can be miniaturized.

  The eddy current type metal sensor according to the present invention is characterized in that components of the first oscillation circuit and the second oscillation circuit are common except for the first coil and the second coil.

  In the eddy current type metal sensor of the present invention, in the first oscillation circuit and the second oscillation circuit, the other components except the first coil and the second coil are common. Therefore, the oscillation frequency measured by each of the first oscillation circuit and the second oscillation circuit is not affected by variations in characteristics due to different components other than the coil, and an accurate value is measured. Therefore, the detection accuracy of eddy current is high.

  The eddy current type metal sensor according to the present invention includes a substrate on which the first coil is disposed on one surface and the second coil is disposed on the other surface.

  In the eddy current type metal sensor of the present invention, the first coil is formed on one surface of the substrate, and the second coil is formed on the other surface of the substrate. Therefore, the coaxial arrangement of the first coil and the second coil can be realized with a simple configuration.

  The eddy current type metal sensor according to the present invention is characterized in that the reference time signal is a clock signal of the external device.

In the present invention, the reference time signal from the external device is a clock signal of the external device, and the measurement unit oscillates in the first oscillation circuit and the second oscillation circuit based on the clock signal of the external device. Measure.
An accurate eddy current can be obtained by using an external clock signal as a reference time signal.

  In the eddy current type metal sensor according to the present invention, the reference time signal is a signal obtained by multiplying a clock signal of the external device.

In the present invention, the reference time signal from the external device is a signal obtained by multiplying the clock signal of the external device, and the measurement unit performs the first oscillation circuit and the second oscillation circuit based on the multiplied clock signal. Measure the oscillation frequency at.
The sensitivity of the eddy current metal sensor can be adjusted by multiplying the clock signal.

  In the eddy current type metal sensor according to the present invention, the reference time signal is a control signal representing a measurement period of an oscillation frequency by the measurement unit based on a clock signal of the external device.

In the present invention, the reference time signal from the external device is a control signal that represents a measurement period of the oscillation frequency based on the clock signal of the external device, and the measurement unit performs the first operation based on the control signal. The oscillation frequency in the oscillation circuit and the second oscillation circuit is measured.
A highly accurate measurement can be performed based on an external clock signal.

  The eddy current type metal sensor according to the present invention includes a processing unit that performs a multiplication process on the reference time signal received by the receiving unit.

In the present invention, the processing unit includes, for example, a PLL (Phase Locked Loop) circuit, and multiplies the reference time signal received by the receiving unit.
The sensitivity of the eddy current metal sensor can be adjusted by multiplying the clock signal.

  The eddy current type metal sensor according to the present invention is characterized in that the detection sensitivity of the presence or absence of a detection object or the measurement sensitivity of the distance to the detection object can be adjusted.

  In the present invention, for example, since the reference time signal received by the receiving unit can be multiplied by the processing unit, the frequency (interval) of the measurement of the oscillation frequency by the measuring unit can be changed, The detection sensitivity of the presence or absence of an object or the measurement sensitivity of the distance to an object to be detected can be adjusted.

  The eddy current detection method according to the present invention is an eddy current detection method for detecting an eddy current of a metal object to be detected, wherein the first coil and the second coil are arranged at different distances from the object to be detected. An oscillation circuit that receives a reference time signal representing time from an external device and oscillates including the first coil and an oscillation circuit that oscillates including the second coil based on the reference time signal The oscillation frequency is measured, the difference between the measured oscillation frequencies is calculated, and the calculated difference is converted as the amount of change in the eddy current of the detected object.

  In the present invention, the eddy current of the object to be detected (metal) can be detected accurately and more accurately even if the external environment such as temperature changes, despite the small and simple configuration. Based on the detection result of the eddy current, it is possible to correctly detect the presence or absence of metal or to measure the distance to the metal with high accuracy. Moreover, the detection sensitivity of the presence or absence of the detection object or the measurement sensitivity of the distance to the detection object can be easily adjusted.

It is a perspective view which shows the structure of the eddy current type metal sensor which concerns on this Embodiment. It is sectional drawing which shows the structure of the eddy current type metal sensor which concerns on this Embodiment. It is sectional drawing which shows the positional relationship of the eddy current type metal sensor which concerns on this Embodiment, and the metal which is a to-be-detected object. It is a block diagram which shows the function structure of the eddy current type metal sensor which concerns on this Embodiment. It is a circuit diagram which shows the example of 1 structure of the eddy current type metal sensor which concerns on this Embodiment. It is a timing chart for demonstrating operation | movement of the eddy current type metal sensor which concerns on this Embodiment. It is a flowchart for demonstrating operation | movement of the eddy current type metal sensor which concerns on this Embodiment. It is sectional drawing which shows the structure of the eddy current type metal sensor in a 1st modification. It is sectional drawing which shows the structure of the eddy current type metal sensor in a 2nd modification. It is sectional drawing which shows the structure of the eddy current type metal sensor in a 3rd modification.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. 1 and 2 are a perspective view and a cross-sectional view showing a configuration of the eddy current type metal sensor according to the present embodiment.

  1 and 2, reference numeral 10 denotes a flat rectangular substrate. A first coil 1 is formed on one surface (the lower surface in the drawing) of one end portion in the longitudinal direction of the substrate 10 (see FIG. 2). A second coil 2 is formed on the other surface (upper surface in the drawing) of the one end of the substrate 10 so as to be coaxial with the first coil 1. The first coil 1 and the second coil 2 are formed, for example, by printing a copper foil pattern on the substrate 10.

  A connector 3 is mounted on the upper surface of the other end portion in the longitudinal direction of the substrate 10 such that a part thereof protrudes from the edge of the other end portion in the longitudinal direction. On the upper surface of the central portion of the substrate 10, an electronic chip 4 composed of a microcomputer for performing various processes described later is mounted. Further, a circuit component 5 is mounted in the vicinity of the electronic chip 4. The circuit component 5 includes a capacitor for forming an oscillation circuit with the first coil 1 or the second coil 2. The eddy current type metal sensor 20 according to the present embodiment is configured as described above.

  FIG. 3 is a cross-sectional view showing the positional relationship between the eddy current type metal sensor 20 according to the present embodiment and the metal that is the object to be detected. On one surface (lower surface) side of the substrate 10, a metal 30 to be detected is disposed so as to face the eddy current metal sensor 20. In this arrangement example, the first coil 1 is arranged closer to the metal 30 (detected object) than the second coil 2.

  FIG. 4 is a block diagram showing a functional configuration of the eddy current type metal sensor 20 according to the present embodiment. In FIG. 4, the same or similar parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

  The first coil 1 and a part of the circuit component 5 constitute a first oscillation circuit 6, and the second coil 2 and a part of the circuit component 5 constitute a second oscillation circuit 7. In the eddy current type metal sensor 20 according to the present embodiment, in the first oscillating circuit 6 and the second oscillating circuit 7, the other constituent members except the first coil 1 and the second coil 2 are common. Therefore, the number of parts can be reduced. Furthermore, the oscillation frequency measured by each of the first oscillation circuit 6 and the second oscillation circuit 7 is not affected by the characteristic variation due to different constituent members, and an accurate value is measured. Therefore, the detection accuracy of the eddy current of the metal 30 is high.

  The electronic chip 4 includes a measurement unit 41 that measures the oscillation frequency in each of the first oscillation circuit 6 and the second oscillation circuit 7, a calculation unit 42 that calculates a difference between the oscillation frequencies measured by the measurement unit 41, and a calculation unit. It has functionally the conversion part 43 which converts the difference calculated in 42 as a change amount of the eddy current of the metal 30 (detected object).

  Furthermore, the circuit component 5 includes, for example, a processing unit 50 having a PLL circuit, and the processing unit 50 multiplies a reference time signal representing time received by a fifth terminal (receiving unit) described later. Can be done. Based on the reference time signal multiplied by the processing unit 50 in this way, the measurement unit 41 measures the oscillation frequency.

  FIG. 5 is a circuit diagram showing a configuration example of the eddy current type metal sensor 20 according to the present embodiment. In FIG. 5, the coil L1 and the coil L2 correspond to the first coil 1 and the second coil 2 described above, respectively. The microcomputer U1 corresponds to the electronic chip 4 described above.

  One end of the coil L1 is connected to the sixth terminal of the microcomputer U1, and one end of the coil L2 is connected to the third terminal of the microcomputer U1. The other end of the coil L1 and the other end of the coil L2 are connected to the base of the transistor Q1 via the capacitor C1. A resistor R2 is provided between the base and collector of the transistor Q1, and a capacitor C2 is provided between the base and emitter of the transistor Q1. The collector of the transistor Q1 is connected to the second terminal of the microcomputer U1 and is grounded through the resistor R3.

  The first terminal of the microcomputer U1 is connected to the input terminal for the power supply voltage Vdd. The input terminal of the power supply voltage Vdd is connected to the emitter of the transistor Q1 through the resistor R1. One end of a capacitor C3 is connected between the resistor R1 and the emitter of the transistor Q1, and the other end of the capacitor C3 is grounded. One end of a capacitor C6 is connected between the input terminal of the power supply voltage Vdd and the first terminal, and the other end of the capacitor C6 is grounded. A grounding terminal is connected to the eighth terminal of the microcomputer U1.

  An output terminal that outputs a detection voltage Vout corresponding to an eddy current is connected to the seventh terminal of the microcomputer U1 via a resistor R4. One end of a capacitor C7 is connected between the output terminal and the resistor R4, and the other end of the capacitor C7 is grounded. The fourth terminal of the microcomputer U1 is connected to an input terminal for inputting a control voltage Vcont for performing offset control via a resistor R6. One end of a capacitor C5 is connected between the fourth terminal of the microcomputer U1 and the resistor R6, and the other end of the capacitor C5 is grounded.

  Furthermore, the clock signal output terminal 101 of the external device is connected to the fifth terminal of the microcomputer U1 via the resistor R5. One end of a capacitor C4 is connected between the fifth terminal and the resistor R5, and the other end of the capacitor C4 is grounded. For example, the eddy current type metal sensor 20 is mounted on the external device.

  A general apparatus that performs various kinds of digital processing incorporates a high-precision oscillator that generates a clock signal. In general, spread spectrum or the like is applied to a clock signal generated by an oscillator included in such a device as a measure against so-called EMI.

  In the eddy current type metal sensor 20 according to the present embodiment, a clock signal (hereinafter also referred to as a reference time signal) generated by an oscillator of an external device as an example and not subjected to spread spectrum or the like is also referred to as a microcomputer. The fifth terminal of U1 is configured to be able to receive. That is, the fifth terminal of the microcomputer U1 is assigned to the receiving terminal (receiving unit) for the clock signal. Based on the received reference time signal, the measurement unit 41 measures the oscillation frequency. In addition, when the fifth terminal of the microcomputer U1 receives the reference time signal from an external device, the processing unit 50 performs a process of multiplying the frequency of the received reference time signal, based on the multiplied reference time signal. Thus, the measurement unit 41 may be configured to measure the oscillation frequency. That is, the reference time signal may be a signal obtained by multiplying the clock signal of the external device. Note that such multiplication processing may be performed by the eddy current metal sensor 20 as described above, or may be performed by the external device.

  The coil L1, the two capacitors C2 and C3, and the transistor Q1 constitute the first oscillation circuit 6 (Colpitts oscillation circuit). The coil L2, the two capacitors C2 and C3, and the transistor Q1 described above. A second oscillation circuit 7 (Colpitts oscillation circuit) is configured. Then, by the switching operation of the microcomputer U1 (the switching operation is performed at the third terminal and the sixth terminal of the microcomputer U1), the first oscillation circuit 6 and the second oscillation circuit 7 oscillate alternately at predetermined time intervals. It is like that.

  Next, the operation of the eddy current type metal sensor 20 according to the present embodiment will be described. FIG. 6 is a timing chart for explaining the operation of the eddy current type metal sensor 20 according to the present embodiment.

  The first oscillating circuit 6 and the second oscillating circuit 7 are alternately oscillated for a predetermined time, and the measuring unit 41 measures the oscillation frequency in each oscillation using the reference time signal from the external device. The predetermined time is 2 ms, for example. Specifically, a control signal representing the start timing and end timing (see arrows in FIG. 6) of the measurement by the measurement unit 41 is generated using the reference time signal, and the measurement unit 41 performs the first operation according to the control signal. The oscillation frequency in the oscillation circuit 6 and the second oscillation circuit 7 is measured.

  At this time, as shown in FIG. 6, in the period in which the first oscillation circuit 6 is oscillated and the oscillation frequency is measured, the second oscillation circuit 7 is not oscillated, and the second oscillation circuit 7 is oscillated and the oscillation is performed. The first oscillation circuit 6 is not oscillated during the frequency measurement period. Therefore, since the oscillation frequency is measured without being influenced by oscillation, the measured value is highly accurate.

  When the measurement of the oscillation frequency for each predetermined time (for example, 2 ms) is finished, the oscillation frequency measured in the first oscillation circuit 6 (derived from the first coil 1) and the oscillation frequency in the second oscillation circuit 7 (in the second coil 2) The difference from the measured oscillation frequency is calculated by the calculation unit 42. Then, the conversion unit 43 converts the calculated difference as an eddy current change amount.

  Further, in the period in which the first oscillation circuit 6 is oscillated and the oscillation frequency is measured, the difference between the previous measurement values (for example, A ′ and B ′) of the first oscillation circuit 6 and the second oscillation circuit 7 is calculated as follows: The calculation unit 42 calculates the difference, and the conversion unit 43 converts the calculated difference into an eddy current to obtain the eddy current change amount. Therefore, the eddy current change amount is calculated at the timing of starting the measurement of the oscillation frequency of each oscillation circuit. Updates are made sequentially.

  FIG. 7 is a flowchart for explaining the operation of the eddy current type metal sensor 20 according to the present embodiment. In the following, for convenience of explanation, a case where the clock signal of the external device 100 is used will be described as an example.

  First, the external device 100 transmits a clock signal generated by its own oscillator to the eddy current metal sensor 20 (step S101), and the eddy current metal sensor 20 receives the clock signal.

  Generally, since such a clock signal often has a high frequency, the processing unit 50 performs a multiplication process on the received clock signal (step S201). However, the eddy current metal sensor 20 according to the present embodiment is not limited to this, and may receive a clock signal that has already been multiplied by the external device 100. In this case, the multiplication process by the processing unit 50 may be omitted.

  Furthermore, in the eddy current type metal sensor 20 according to the present embodiment, the detection sensitivity of the eddy current is increased by receiving a clock signal having a different frequency or by changing an integral multiple of the multiplication processing by the processing unit 50. It can be adjusted.

  Next, the measurement unit 41 uses the multiplied clock signal as a reference time signal, and based on this, oscillates the first oscillation circuit 6 and the second oscillation circuit 7 alternately for a predetermined time and measures the oscillation frequency (step) S202).

  Further, the calculation unit 42 calculates a difference between the oscillation frequency measured by the first oscillation circuit 6 and the oscillation frequency measured by the second oscillation circuit 7 (step S203).

  Further, the conversion unit 43 converts the difference calculated by the calculation unit 42 as an eddy current change amount (that is, voltage output) (step S204). Thereby, based on the converted eddy current, it is possible to detect the presence or absence of the detection object (metal 30) and to measure the distance to the detection object.

  Thereafter, the detection result by the eddy current type metal sensor 20 is transmitted to, for example, the external device 100 (step S205) and output via a display unit (not shown) of the external device 100 (step S102).

  The eddy current metal sensor 20 according to the present embodiment is not limited to the above description. For example, a determination unit (not shown) that determines whether the frequency of the clock signal received from the external device 100 is equal to or higher than a predetermined threshold is provided, and only when the determination unit determines that the frequency is higher than the predetermined threshold. You may comprise so that such a multiplication process may be performed.

  In this embodiment, there are the following advantages. The magnitude of the eddy current varies depending on the type of metal 30 that is the detection target. In this case, for example, by using an unused terminal of the microcomputer U1 and controlling the voltage level of the unused terminal from the outside, an offset function for adjusting sensitivity can be provided.

  Note that although FIG. 5 shows a microcomputer having eight terminals as an example, it is not limited to this configuration. If necessary, it is possible to use a microcomputer with a different number of terminals to transmit information such as changes in eddy currents to the upper control side using means such as serial communication, and to receive control signals from the upper side. is there.

  Hereinafter, the principle that an eddy current can be detected by the procedure as described above will be described. Further, based on the detection result of the eddy current, the presence / absence of the object to be detected (metal 30) can be detected and the distance to the object to be detected (metal 30) can be measured.

  When the eddy current of the object to be detected increases, the inductance of the coil disposed in the vicinity of the object to be detected decreases according to the fluctuation of the eddy current. As a result, the oscillation frequency of the oscillation circuit including the coil increases. Here, when two coils are arranged at different distances from the object to be detected, the inductance of each coil decreases, and the oscillation frequency of any oscillation circuit increases. However, the coil closer to the object to be detected is more affected by changes in eddy currents than the coil farther away. Therefore, in the above case, the amount of decrease in inductance increases and the amount of increase in oscillation frequency also increases. Become. Therefore, a difference corresponding to the degree of change in the eddy current occurs in the oscillation frequency in the two oscillation circuits including the two coils. Thus, since there is a correlation between the difference between the two oscillation frequencies and the eddy current, in this embodiment, the eddy current of the object to be detected is detected based on the difference between the oscillation frequencies of the two oscillation circuits. It is possible. Based on the detected eddy current of the detected object, it is possible to detect the presence or absence of the detected object (metal 30) or measure the distance to the detected object (metal 30).

  In the eddy current type metal sensor 20 in the above-described embodiment, the first coil 1 corresponds to a coil closer to the detected object (metal 30), and the second coil 2 corresponds to the detected object. This corresponds to the coil farther away from (metal 30).

  According to the eddy current type metal sensor 20 according to the present embodiment, an eddy current generated in a metal can be detected. Therefore, it can be used as a presence sensor for detecting the presence or absence of metal. Moreover, it can be used as a distance sensor for measuring a distance from a metal. It can also be used as a rotation speed detection sensor and a proximity switch.

  In the above-described embodiment, the two oscillation circuits are driven based on the change in inductance of the two coils (the first coil 1 and the second coil 2) coaxially arranged on the substrate 10 based on the reference time signal. The difference between the oscillation frequencies in the first oscillation circuit 6 and the second oscillation circuit 7 is detected, and the difference (amount of change in oscillation frequency) is processed by the microcomputer U1 to detect a change in eddy current. . Here, the two coils are alternately connected to the oscillation circuit, and based on the reference time signal, the oscillation frequency is measured alternately by the microcomputer U1 over a predetermined time, and the difference is calculated to calculate the eddy current. Changes are detected.

  In the present embodiment, since the first coil 1 and the second coil 2 are coaxially arranged on the upper and lower surfaces of the substrate 10, the area necessary for the arrangement of the coils can be reduced and the horizontal size can be reduced. . In addition, since the coil is formed by printing the conductor pattern on the substrate 10, it is possible to reduce the height in the height direction (the thickness direction of the substrate 10). Furthermore, since various processes are performed using a microcomputer, the number of components can be reduced and the area for mounting circuit components can be reduced. From the above, the eddy current type metal sensor can be significantly reduced in size.

  Since the measurement of the oscillation frequency in the two oscillation circuits is alternately performed, the measurement of the oscillation circuit including one coil is not affected by the magnetic flux generated in the other coil (inductance change in the other coil). Therefore, an accurate oscillation frequency can be measured, and as a result, eddy current can be detected with high accuracy.

  In this embodiment, since the transistors and capacitors constituting the two oscillation circuits are shared, and the coils are arranged in the oscillation circuits, the number of parts can be reduced and the cost can be reduced. In addition, since the number of parts is small, variations in part characteristics can be reduced, and further accurate measurement is possible without being affected by disturbances such as temperature changes and noise.

  Since various processes are performed by software using a microcomputer, the number of circuit parts as hardware can be reduced and the influence of variations in characteristics of circuit parts is reduced. In addition, since it is processed by software, it is less affected by the environment (temperature, humidity, etc.). Therefore, the accuracy of the detected eddy current can be increased.

  Further, even when the type of metal 30 to be detected is different, it can be easily dealt with only by changing the contents of the software. Therefore, mass production becomes easy and cost reduction can be achieved.

  Furthermore, in the eddy current type metal sensor 20 according to the present embodiment, the control signal, that is, the measurement time for measuring the oscillation frequency can be changed by changing the reference time signal. The presence / absence detection sensitivity or the measurement sensitivity of the distance to the object can be easily adjusted. More specifically, the clock signal of the external device 100 may be appropriately processed (for example, multiplied) by the external device 100, and the clock signal received from the external device 100 is multiplied by the eddy current metal sensor 20. You may give it.

  In the above description, the case where the reference time signal is the clock signal of the external apparatus 100 as it is and the case where the reference signal is subjected to multiplication processing have been described. However, the present embodiment is not limited to this. For example, the reference time signal may be a control signal representing the start time and / or end time of the measurement of the oscillation frequency by the measurement unit 41 based on the clock signal of the external device 100. That is, a control signal used for measuring the oscillation frequency by the measuring unit 41 may be generated by the eddy current metal sensor 20 or the external device 100 based on the clock signal of the external device 100.

  In the above-described embodiment, the first coil 1 and the second coil 2 are formed coaxially by printing conductor patterns on the upper surface and the lower surface of the substrate 10, respectively. The forming method 2 is not limited to this, and may be another method. Hereinafter, these other methods will be described as modified examples.

(First modification)
FIG. 8 is a cross-sectional view showing the configuration of the eddy current type metal sensor in the first modification. 8, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the first modification, the first coil 1 and the second coil 2 are formed on the lower surface of the substrate 10 by coaxial pattern lamination with an insulating layer interposed therebetween, for example, by pattern printing of copper foil. Further, no coil is formed on the upper surface of the substrate 10, and the electronic chip 4, the circuit component 5, and the connector 3 similar to those of the above-described embodiment are mounted. The first coil 1 and the second coil 2 are formed immediately below the mounting position of the electronic chip 4 and the circuit component 5. Therefore, further downsizing of the configuration of the eddy current type metal sensor can be achieved. Unlike the configuration shown in FIG. 8, the concentric first coil 1 and second coil 2 described in the first modification are formed immediately below the mounting positions of the electronic chip 4 and the circuit component 5. You may do it.

(Second modification)
FIG. 9 is a cross-sectional view showing the configuration of the eddy current type metal sensor in the second modification. 9, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the second modification, a first coil 1 is formed by mounting a separate air core coil on the lower surface of one end portion of the substrate 10, and coaxial with the first coil 1 on the upper surface of one end portion of the substrate 10. The second coil 2 is formed by mounting a separate air core coil. In the remaining area on the upper surface of the substrate 10, the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted.

(Third Modification)
FIG. 10 is a cross-sectional view showing the configuration of the eddy current metal sensor in the third modification. 10, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the third modification, the first coil 1 and the second coil 2 are formed by stacking and mounting two air core coils of different parts on the upper surface of one end of the substrate 10. In the remaining area on the upper surface of the substrate 10, the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted. Note that, unlike the configuration shown in FIG. 10, the first coil 1 and the second coil 2 that form the stacked configuration of the two air-core coils as described above may be formed on the lower surface of the substrate 10.

  In the present invention, it is utilized that the amount of inductance change of the coil closer to the object to be detected is increased by arranging the coils with the same size (diameter) and changing the distance to the metal to be measured. The eddy current is detected, but it is only necessary to have a difference in the amount of change in inductance between the coils. Can be possible.

  The disclosed embodiments should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 1st coil 2 2nd coil 3 Connector 4 Electronic chip 5 Circuit component 6 1st oscillation circuit 7 2nd oscillation circuit 10 Board | substrate 20 Eddy current type metal sensor 30 Metal (to-be-detected object)
41 measurement unit 42 calculation unit 43 conversion unit 50 processing unit

Claims (11)

In an eddy current type metal sensor that detects eddy currents of metal objects,
A first oscillation circuit that oscillates including the first coil;
A second oscillation circuit that oscillates including the second coil;
A receiving unit for receiving a reference time signal representing time from an external device;
A measurement unit for measuring an oscillation frequency in each of the first oscillation circuit and the second oscillation circuit based on the reference time signal;
A calculation unit for calculating a difference between oscillation frequencies measured by the measurement unit;
An eddy current type metal sensor comprising: a conversion unit that converts the difference calculated by the calculation unit as a change amount of the eddy current of the detected object.   2. The eddy current metal sensor according to claim 1, wherein the measurement unit is configured to alternately measure an oscillation frequency in the first oscillation circuit and an oscillation frequency in the second oscillation circuit. .   The eddy current metal sensor according to claim 1, wherein the first coil and the second coil are arranged coaxially.   The component of the said 1st oscillation circuit and the 2nd oscillation circuit is common except the said 1st coil and the 2nd coil, The eddy current type | formula as described in any one of Claim 1 to 3 characterized by the above-mentioned. Metal sensor.   The eddy current type metal sensor according to any one of claims 1 to 4, further comprising a substrate on which the first coil is disposed on one surface and the second coil on the other surface.   The eddy current type metal sensor according to any one of claims 1 to 5, wherein the reference time signal is a clock signal of the external device.   The eddy current type metal sensor according to any one of claims 1 to 5, wherein the reference time signal is a signal obtained by multiplying a clock signal of the external device.   The eddy current type according to any one of claims 1 to 5, wherein the reference time signal is a control signal representing a measurement period of an oscillation frequency by the measurement unit based on a clock signal of the external device. Metal sensor.   The eddy current metal sensor according to claim 6, further comprising a processing unit that performs a multiplication process on the reference time signal received by the receiving unit.   10. The eddy current metal sensor according to claim 9, wherein the detection sensitivity of the presence or absence of the detection object or the measurement sensitivity of the distance to the detection object is adjustable. In an eddy current detection method for detecting an eddy current of a metal object,
Disposing the first coil and the second coil at different distances from the object to be detected;
A reference time signal representing time is received from an external device,
Based on the reference time signal, the oscillation frequency of the oscillation circuit that oscillates including the first coil and the oscillation frequency of the oscillation circuit that oscillates including the second coil are respectively measured.
Calculate the difference between the measured oscillation frequencies,
An eddy current detection method, wherein the calculated difference is converted as an amount of change in eddy current of the detected object.

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