JP2018119830A - Eddy current metal sensor and method for detecting eddy current - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current metal sensor which can accurately detect an eddy current of a detection object made of metal and the presence or absence of metal and can precisely measure the distance to the metal in spite of being small-sized and having a simple configuration, and a method for accurately detecting an eddy current of a detection object made of metal.SOLUTION: The present invention includes: a first coil 1 and a second coil 2; a first oscillation circuit 6, which oscillates by including the first coil 1; a second oscillation circuit 7, which oscillates by including the second coil 2; a measuring unit 41 for measuring the respective oscillation frequencies of the first and second oscillation circuits 6 and 7; a calculation unit 42 for calculating the difference between the oscillation frequencies measured by the measuring unit 41; and a conversion unit 43 for converting the difference calculated by the calculation unit 42 into 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 a magnetic field generated by a coil of the sensor. 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.

  The present invention has been made in view of such circumstances, and even in a small and simple configuration, without being affected by the external environment, accurately detecting the eddy current of a detection object made of metal, An object of the present invention is to provide an eddy current type metal sensor capable of detecting the presence / absence of a metal and measuring a distance to the metal with high accuracy, and an eddy current detection method capable of accurately detecting an eddy current of a detection object made of metal. And

  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 measurement unit that measures an oscillation frequency in each of the first oscillation circuit and the second oscillation circuit, a calculation unit that calculates a difference between oscillation frequencies measured by the measurement unit, and the calculation unit And a conversion unit that converts the difference calculated in step 1 into an eddy current of the detected object.

  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. The calculation unit calculates a difference between the two oscillation frequencies measured by the measurement unit, and the conversion unit converts the difference calculated by the calculation unit into an 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 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. 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 measured, and the difference between the measured oscillation frequencies is calculated. Is converted into an eddy current of the object to be detected.

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

It is a perspective view which shows the structure of the eddy current type metal sensor of this invention. It is sectional drawing which shows the structure of the eddy current type metal sensor of this invention. It is sectional drawing which shows the positional relationship of the eddy current type metal sensor of this invention 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 of this invention. It is a circuit diagram which shows one structural example of the eddy current type metal sensor of this invention. It is a flowchart which shows the operation | movement procedure of the eddy current detection method of this invention. It is a timing chart for demonstrating operation | movement of the eddy current type metal sensor of this invention. It is a perspective view which shows the structure of the coil 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. It is sectional drawing which shows the structure of the eddy current type metal sensor in a 4th 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 the configuration of the eddy current type metal sensor of the present invention.

  1 and 2, reference numeral 10 denotes a flat rectangular substrate. A first coil 1 is formed on one surface (lower surface) of one end of the substrate 10 (see FIG. 2). A second coil 2 is formed on the other surface (upper surface) of 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 of the substrate 10 with a part protruding from the other end. 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 of the present invention is configured as described above.

  FIG. 3 is a cross-sectional view showing the positional relationship between the eddy current type metal sensor 20 of the present invention 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 of the present invention. 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 of the present invention, in the first oscillation circuit 6 and the second oscillation circuit 7, the other components except the first coil 1 and the second coil 2 are common. Therefore, 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 into the eddy current of the metal 30 (detected object).

  FIG. 5 is a circuit diagram showing one configuration example of the eddy current type metal sensor 20 of the present invention. 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. An input terminal for inputting a control voltage Vcont for performing offset control is connected to the fifth terminal of the microcomputer U1 via a resistor R6. One end of a capacitor C4 is connected between the fifth terminal of the microcomputer U1 and the resistor R6, and the other end of the capacitor C4 is grounded.

  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 of the present invention will be described. FIG. 6 is a flowchart showing the operation procedure of the eddy current detection method of the present invention, and FIG. 7 is a timing chart for explaining the operation of the eddy current type metal sensor 20 of the present invention.

  The first oscillation circuit 6 and the second oscillation circuit 7 are alternately oscillated for a predetermined time, and the oscillation frequency in each oscillation is measured by the measurement unit 41 (step S1). The predetermined time is 2 ms, for example. At this time, as shown in FIG. 7, the second oscillation circuit 7 is not oscillated during the period in which the first oscillation circuit 6 is oscillated and the oscillation frequency is measured, and the second oscillation circuit 7 is oscillated to oscillate the oscillation. 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) A difference from the measured oscillation frequency is calculated by the calculation unit 42 (step S2). Then, the conversion unit 43 converts the calculated difference into an eddy current to obtain an eddy current change amount (step S3).

  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.

  The present invention has 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, the present invention can detect the eddy current of the object to be detected based on the difference between the oscillation frequencies of the two oscillation circuits. 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 invention, eddy current generated in 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 change in inductance of the two coils (the first coil 1 and the second coil 2) coaxially arranged on the substrate 10 is determined by the accuracy of the oscillator built in the microcomputer (electronic chip 4). Is detected as a difference in oscillation frequency between two oscillation circuits (first oscillation circuit 6 and second oscillation circuit 7) driven by a simple clock signal, and the difference (amount of change in oscillation frequency) is processed by a microcomputer. Changes in eddy currents are detected. Here, the two coils are alternately connected to the oscillation circuit, the oscillation frequency is measured alternately by a microcomputer for a predetermined time, and the difference is calculated to detect the change in eddy current.

  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 narrowing in the horizontal direction can be achieved. . Further, since the coil is formed by printing the conductor pattern on the substrate 10, the height in the height direction can be reduced. 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.

  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 perspective view showing the configuration of the coil 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 FIG. 8, the upper and lower surfaces of the substrate 10 are shown opposite to those in FIG. In the first modification, the first coil 1 and the second coil 2 are formed concentrically on the lower surface of the substrate 10 by, for example, pattern printing of copper foil. A coil is not 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 in the above-described embodiment are mounted.
The first coil 1 is smaller than the second coil 2 and can be regarded as being in a position where the distance from the object to be detected is pseudo far away from the second coil 2.

(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, the first coil 1 and the second coil 2 are formed on the lower surface of the substrate 10 in a coaxial manner 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. 9, 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.

(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, 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 is 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.

(Fourth modification)
FIG. 11 is a cross-sectional view illustrating a configuration of an eddy current metal sensor according to a fourth modification. In FIG. 11, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the fourth 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. In addition, unlike the structure shown in FIG. 11, you may make it form the 1st coil 1 and the 2nd coil 2 which make the laminated structure of the above two air-core coils in the lower surface of the board | substrate 10. FIG.

  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

Claims (6)

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 measurement unit for measuring an oscillation frequency in each of the first oscillation circuit and the second oscillation circuit;
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 into an eddy current of the object to be detected.   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. 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;
Measure 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, respectively.
Calculate the difference between the measured oscillation frequencies,
An eddy current detection method comprising converting the calculated difference into an eddy current of the object to be detected.

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