JP2019144138A - Eddy current type metal sensor and method for detecting eddy current - Google Patents

Abstract

To provide an eddy current type metal sensor which can accurately detect an eddy current of a detection target object of metal and the presence of metal and also can measure the distance to the metal in spite of the small size and the simple configuration of the sensor, and a method for detecting an eddy current which can be used to precisely detect an eddy current of a detection target object of metal.SOLUTION: The present invention includes; a first oscillation circuit 6 for oscillating with a first coil 1 therein; a second oscillation circuit 7 for oscillating with a second coil 2 therein; a measurement unit 41 for measuring the respective oscillation frequencies in the first oscillation circuit 6 and in the second oscillation circuit 7; an adjusting unit for adjusting at least one of the time it takes for the measurement unit to measure the number of oscillation pulses in the first oscillation circuit and the time it takes for the measurement unit to measure the number of oscillation pulses in the second oscillation circuit; a calculation unit 43 for calculating the difference between the oscillation frequencies obtained by the measurement unit 41; and a converter 44 for converting the difference calculated by the calculation unit 43 into the eddy current of the detection target object.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, To provide an eddy current type metal sensor capable of detecting the presence / absence of metal, measuring the 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. Objective.

  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 the number of oscillation pulses in each of the first oscillation circuit and the second oscillation circuit, a measurement time of the number of oscillation pulses in the first oscillation circuit by the measurement unit, and An adjustment unit that adjusts at least one of the measurement times of the number of oscillation pulses in the second oscillation circuit by the measurement unit, a calculation unit that calculates a difference in the number of oscillation pulses measured by the measurement unit, and a calculation by the calculation unit And a conversion unit that converts the difference obtained into the eddy current of the object to be detected.

  In the present invention, the number of oscillation pulses means the number of pulses within a predetermined measurement time at each oscillation frequency oscillated in each oscillation circuit. Therefore, if the measurement time is the same, the difference in the number of oscillation pulses can be regarded as synonymous with the difference in oscillation frequency.

  In the eddy current type metal sensor of the present invention, the number of oscillation pulses of the first oscillation circuit including the first coil arranged in the vicinity of the detected object and the first coil in the vicinity of the detected object are the detected object. The number of oscillation pulses of the second oscillation circuit including the second coil arranged with different distances to is measured by the measurement unit. The calculation unit calculates a difference between both oscillation pulses 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 number of oscillation pulses 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, the fluctuation in the number of oscillation pulses in the oscillation circuit also increases. Therefore, the eddy current can be detected from the difference in the number of oscillation pulses by each oscillation circuit 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.

  Here, at least one of the first measurement time for measuring the number of oscillation pulses of the first oscillation circuit and the second measurement time for measuring the number of oscillation pulses of the second oscillation circuit is adjusted by the adjustment unit. Specifically, when the distance from the object to be detected is shorter in the first coil than in the second coil, the inductance of the first coil is larger than the inductance of the second coil, and the number of oscillation pulses of the first oscillation circuit is Since the number is smaller than the number of oscillation pulses of the second oscillation circuit, the first measurement time is adjusted to be relatively longer than the second measurement time, and the number of oscillation pulses is adjusted to be the same. By performing such adjustment, the influence of temperature fluctuation during actual detection is reduced.

  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 (the number of pulses in a certain time is large). As a result, since the number of clocks within a certain time of the computer is less than the number of oscillation pulses, in the case of measuring the number of oscillation pulses, the measurement time for obtaining the same resolution can be shortened and the measurement time can be made constant.

  In addition, a series of processes for measuring the number of oscillation pulses, calculating the difference between the oscillation pulses, and converting the 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.

  In the eddy current type metal sensor according to the present invention, the measurement unit is configured to alternately measure the number of oscillation pulses in the first oscillation circuit and the number of oscillation pulses in the second oscillation circuit. Features.

  In the eddy current type metal sensor of the present invention, the measurement of the number of oscillation pulses in the first oscillation circuit and the measurement of the number of oscillation pulses in the second oscillation circuit are alternately performed while switching. Therefore, when the number of oscillation pulses in one oscillation circuit is measured, the other oscillation circuit is not oscillating, so the measurement value of the number of oscillation pulses in one oscillation circuit is not affected by the oscillation of the other oscillation circuit. Therefore, the exact number of oscillation pulses 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 number of oscillation pulses measured by each of the first oscillation circuit and the second oscillation circuit is not affected by characteristic variations caused by different constituent members 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.

  An eddy current detection method according to the present invention is an eddy current detection method for detecting an eddy current of an object to be detected made of metal, wherein an assembled coil including a first coil and a second coil having different distances from the object to be detected is provided. The first oscillation circuit is arranged to measure the number of oscillation pulses of a first oscillation circuit that oscillates including the first coil and the number of oscillation pulses of the second oscillation circuit that oscillates including the second coil. And adjusting at least one of a first measurement time for measuring the number of oscillation pulses and a second measurement time for measuring the number of oscillation pulses of the second oscillation circuit, and calculating a difference between the measured number of oscillation pulses. The difference is converted into an eddy current of the detected object.

  In the present invention, the eddy current is detected from the difference in the number of oscillation pulses by the respective oscillation circuits using the two coils (the first coil and the second coil), and based on the detected eddy current, Detection of the presence or absence of a detection object, measurement of the distance to the detection object, and the like can be performed.

  In the eddy current detection method according to the present invention, when the distance of the second coil from the object to be detected is shorter than the distance of the first coil from the object to be detected, the second measurement time is the first measurement time. At least one of the first measurement time and the second measurement time is adjusted so as to be relatively longer than the time.

  In the present invention, the first measurement time is adjusted to be relatively longer than the second measurement time, and the number of oscillation pulses is adjusted to be the same. By performing such adjustment, the influence of temperature fluctuation during actual detection is reduced.

  An eddy current type metal sensor according to the present invention is an eddy current type metal sensor that detects an eddy current of an object made of metal, and oscillates by including a first coil whose inductance changes due to the eddy current of the object to be detected. The first oscillation circuit, the second oscillation circuit that oscillates including the second coil whose inductance changes due to the eddy current of the object to be detected, and the number of oscillation pulses in each of the first oscillation circuit and the second oscillation circuit are measured. A measurement unit; a first adjustment unit that adjusts a measurement time so that the number of oscillation pulses in the first oscillation circuit by the measurement unit becomes a predetermined value; and an oscillation in the first oscillation circuit that is adjusted by the first adjustment unit. At least one of the measurement time of the number of pulses and the measurement time of the number of oscillation pulses in the second oscillation circuit is adjusted based on the number of oscillation pulses measured in a predetermined environment. A calculation unit that calculates a difference between the number of oscillation pulses measured by the measurement unit in a measurement time after adjustment by the first adjustment unit and the second adjustment unit, and a calculation unit And a conversion unit that converts the calculated difference into an eddy current of the detected object.

  In the present invention, the eddy current is detected from the difference in the number of oscillation pulses by the respective oscillation circuits using the two coils (the first coil and the second coil), and based on the detected eddy current, Detection of the presence or absence of a detection object, measurement of the distance to the detection object, and the like can be performed.

  In the eddy current type metal sensor according to the present invention, the second adjustment unit adjusts a measurement time of the number of oscillation pulses in the second oscillation circuit.

  In the present invention, the first oscillation circuit can be operated as a reference.

  In the eddy current type metal sensor according to the present invention, the calculation unit adjusts the measurement time by the first adjustment unit and the second adjustment unit, and then adjusts the first adjustment in the measurement unit under a predetermined environment. And the difference between the number of oscillation pulses measured in the measurement time after adjustment by the second adjustment unit and the difference calculated by the calculation unit, the number of oscillation pulses in the first oscillation circuit and the second oscillation A third adjustment unit that adjusts at least one of the number of oscillation pulses in the circuit is further provided.

  In the present invention, the difference between the number of oscillation pulses measured in the measurement time after adjustment by the first adjustment unit and the second adjustment unit is calculated, and the number of oscillation pulses in the first oscillation circuit is calculated based on the calculated difference, and Since at least one of the number of oscillation pulses in the second oscillation circuit is adjusted, the difference in eddy current can be set to 0 under a predetermined environment that should be the measurement center.

  In the eddy current type metal sensor according to the present invention, the third adjustment unit adjusts the number of oscillation pulses in the second oscillation circuit.

  In the present invention, the first oscillation circuit can be operated as a reference.

  The present invention is realized by using a reference metal plate in an environment.

  In the present invention, by using the reference metal plate, a predetermined eddy current can be set at the center of the measurement range.

  In the eddy current detection method according to the present invention, the reference coil that oscillates including the reference coil by arranging a set coil in which the detection coil and the reference coil are coaxially arranged so that their axes are parallel and overlap in the axial direction. The number of oscillation pulses of the circuit is measured at a predetermined initial measurement time, and a first measurement time obtained by adjusting the initial measurement time is determined so that the measured number of oscillation pulses becomes a predetermined value. The same time as the time is set as the second measurement time, and after the reference metal plate is disposed at a predetermined position near the detection coil, the number of oscillation pulses of the reference oscillation circuit in the first measurement time, and the second measurement time The number of oscillation pulses of the detection oscillation circuit that oscillates including the detection coil is measured, and at least one of the first measurement time and the second measurement time is adjusted based on the two measured oscillation pulse numbers, In an environment where the metal plate is removed and the object to be detected is present, the number of oscillation pulses of the reference oscillation circuit is measured at the first measurement time, and the number of oscillation pulses of the detection oscillation circuit is measured at the second measurement time. An eddy current detection method comprising: calculating a difference in the number of measured oscillation pulses, and converting the calculated difference into an eddy current of the object to be detected.

  In the present invention, the eddy current is detected from the difference in the number of oscillation pulses by the respective oscillation circuits using the two coils (the first coil and the second coil), and based on the detected eddy current, Detection of the presence or absence of a detection object, measurement of the distance to the detection object, and the like can be performed.

  The eddy current detection method according to the present invention is characterized in that the second measurement time is adjusted.

  In the present invention, the first oscillation circuit can be operated as a reference.

  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 an eddy current type metal sensor. It is sectional drawing which shows the structure of an eddy current type metal sensor. It is sectional drawing which shows the positional relationship of an eddy current type metal sensor and the metal which is a to-be-detected object. It is a block diagram which shows the function structure of an eddy current type metal sensor. It is a circuit diagram which shows one structural example of an eddy current type metal sensor. It is a timing chart for demonstrating operation | movement of an eddy current type metal sensor. It is a flowchart which shows the process sequence example of a measurement time adjustment process. It is a flowchart which shows the process sequence example of an initial correction process. It is a flowchart which shows the process example of a correction process. It is a flowchart which shows the process sequence example of a forced correction process. It is a flowchart which shows the process sequence example of a forced correction after the correction | amendment of a correction process. 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, embodiments will be specifically described with reference to the drawings. 1 and 2 are a perspective view and a cross-sectional view showing a configuration of an eddy current type metal sensor.

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

  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 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 of 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 second coil 2 is arranged closer to the metal 30 (object to be detected) than the first coil 1 is.

  FIG. 4 is a block diagram showing a functional configuration of the eddy current type metal sensor 20. 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 embodiment, in the first oscillation circuit 6 and the second oscillation circuit 7, the other constituent members except the first coil 1 and the second coil 2 are common. Therefore, the number of oscillation pulses measured by each of the first oscillation circuit 6 and the second oscillation circuit 7 is not affected by variations in characteristics 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.

  In addition, the electronic chip 4 includes a measuring unit 41 that measures the number of oscillation pulses in each of the first oscillation circuit 6 and the second oscillation circuit 7, and a measurement time (first time) of the number of oscillation pulses in the first oscillation circuit 6 in the measurement unit 41. Adjustment unit (first adjustment unit, second adjustment unit, third adjustment unit) 42 for adjusting at least one of the measurement time (second measurement time) of the oscillation pulse number in the second oscillation circuit 7; A calculation unit 43 that calculates the difference in the number of oscillation pulses measured by the measurement unit 41 and a conversion unit 44 that converts the difference calculated by the calculation unit 43 into an eddy current of the metal 30 (detected object) are functionally provided. doing.

  FIG. 5 is a circuit diagram showing a configuration example of the eddy current type metal sensor 20. 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 embodiment will be described. FIG. 6 is a timing chart for explaining the operation of the eddy current type metal sensor 20 of the present embodiment. The horizontal axis in FIG. 6 is time. The unit of the horizontal axis is, for example, second or millisecond. The vertical axis represents voltage in the upper stage. The upper unit is, for example, millivolts. The vertical axis represents the eddy current value in the lower stage. The lower unit is, for example, milliamps.

  Over the first measurement time adjusted by the adjusting unit 42, the first oscillation circuit 6 is oscillated and the number of oscillation pulses is measured by the measuring unit 41, and the second adjusted by the adjusting unit 42 Over the measurement time, the process of oscillating the second oscillation circuit 7 and measuring the number of oscillation pulses by the measurement unit 41 is performed alternately. At this time, as shown in FIG. 6, in the period in which the first oscillation circuit 6 is oscillated and the number of oscillation pulses is measured, the second oscillation circuit 7 is not oscillated, and the second oscillation circuit 7 is oscillated. The first oscillation circuit 6 is not oscillated during the period in which the number of oscillation pulses is measured. Therefore, since the number of oscillation pulses is measured without being affected by each other, the measured value is highly accurate.

  When the measurement of the number of oscillation pulses for each predetermined time (first measurement time and second measurement time) is completed, the number of oscillation pulses measured (derived from the first coil 1) in the first oscillation circuit 6 and the second oscillation The calculation unit 43 calculates a difference from the measured number of oscillation pulses (derived from the second coil 2) in the circuit 7. Then, the conversion unit 44 converts the calculated difference into an eddy current, and obtains the amount of change in the eddy current.

  Further, during the period in which the first oscillation circuit 6 is oscillated and the number of oscillation pulses 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. The calculation unit 43 calculates the difference, and the conversion unit 44 converts the calculated difference into an eddy current to obtain the amount of change in the eddy current. Therefore, the change in the eddy current at the timing of starting the measurement of the number of oscillation pulses of each oscillation circuit. The quantity is updated sequentially. In FIG. 6, the measurement of the second oscillation circuit 7 is performed across time 0, and the number of oscillation pulses B ′ is obtained. Further, before that, measurement of the first oscillation circuit 6 is performed, and the number of oscillation pulses A ′ is obtained. Therefore, the eddy current value is calculated from the difference (A′−B ′) in the number of oscillation pulses after the time point when the oscillation pulse number B ′ of the second oscillation circuit 7 is obtained. Subsequently, the next measurement of the first oscillation circuit 6 is performed, and the oscillation pulse number A is obtained. Then, an eddy current value is calculated from the difference in the number of oscillation pulses (B′−A). Subsequently, the next measurement of the second oscillation circuit 7 is performed, and the oscillation pulse number B is obtained. Then, an eddy current value is calculated from the difference (A−B) in the number of oscillation pulses. Further, the first oscillation circuit 6 is measured, and the oscillation pulse number A * is obtained. Then, an eddy current value is calculated from the difference in the number of oscillation pulses (B−A *). The above measurement and eddy current value calculation are repeated.

  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 number of oscillation pulses 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 number of oscillation pulses increases in any oscillation circuit. However, the coil closer to the object to be detected is more affected by the change in eddy current than the coil farther away. Therefore, in the above case, the amount of decrease in inductance increases and the amount of increase in the number of oscillation pulses also increases. growing. Therefore, the number of oscillation pulses in the two oscillation circuits each including the two coils has a difference corresponding to the degree of change in eddy current. Thus, since there is a correlation between the difference between the number of oscillation pulses and the eddy current, in this embodiment, the eddy current of the object to be detected is calculated based on the difference between the oscillation pulse numbers of both oscillation circuits. It is possible to detect. 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 farther from the detected object (metal 30), and the second coil 2 corresponds to the detected object. This corresponds to the coil closer to (metal 30). In the present embodiment, a coil closer to the object to be detected is a detection coil, and a coil farther from the object is a reference coil.

  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.

  Here, the adjustment process of at least one of the first measurement time and the second measurement time in the adjustment unit 42 will be described.

  Since the usage environment differs between the first coil 1 close to the detection object and the second coil 2 far from the detection object, the detection characteristics of the eddy current type metal sensor are easily affected by temperature fluctuations. Moreover, since the 1st coil 1 and the 2nd coil 2 are formed by the printing of the copper foil pattern to the board | substrate 10 as mentioned above, the 1st coil 1 and the 2nd coil 2 resulting from the difference in formation conditions. Differences in characteristics are inevitable.

  In order to solve such a problem, the eddy current type metal sensor 20 of the present embodiment adjusts at least one of the first measurement time and the second measurement time. This adjustment process is performed before the actual eddy current detection process is executed, such as when the eddy current metal sensor 20 is shipped or when a distance sensor including the eddy current metal sensor 20 is used. These measurement times are adjusted so that there is no difference in the number of pulses in one measurement period in the first coil 1 and the second coil 2 in the situation of the median value of the desired detection range. In addition, in order to create the situation of the median value of the detection range, a metal plate having a size as the median value is used. At this time, the ambient temperature is a room temperature.

  The second coil 2 disposed at a position close to the detected object is greatly affected by the detected object, and the inductance increases. On the other hand, the first coil 1 arranged at a position far from the object to be detected is hardly affected by the object to be detected and the inductance is not so large. Since the oscillation frequency is almost inversely proportional to the inductance, the number of oscillation pulses of the second oscillation circuit 7 is smaller than the number of oscillation pulses of the first oscillation circuit 6. In view of this, the second measurement time is adjusted to be relatively longer than the first measurement time by compensating for the difference due to the magnitude of the influence of the detected object. Specifically, the measurement time is adjusted so that the number of oscillation pulses of the first oscillation circuit 6 and the number of oscillation pulses of the second oscillation circuit 7 are the same.

  When performing the adjustment such that the second measurement time is relatively longer than the first measurement time, the second measurement time is not changed and the first measurement time is not changed, and the first measurement time is not changed. Either the adjustment for increasing the second measurement time or the adjustment for shortening the first measurement time to increase the second measurement time may be used.

  In adjusting the measurement time, first, the measurement time is assumed to be the same. After the measurement of the number of oscillation pulses by the first oscillation circuit 6 and the measurement of the number of oscillation pulses by the second oscillation circuit 7, the difference is calculated. Measure and adjust either measurement time so that the difference disappears. In this case, the same number of oscillation pulses may not be obtained by adjusting the measurement time once. In this case, the adjustment is performed as follows. Specifically, the number of oscillation pulses by the first oscillation circuit 6 and the number of oscillation pulses by the second oscillation circuit 7 are measured again at the adjusted measurement time, and the difference between the oscillation pulse numbers is calculated so that the difference disappears. Adjust the measurement time of either one. Finally, the state where the difference between the number of oscillation pulses by the first oscillation circuit 6 and the number of oscillation pulses by the second oscillation circuit 7 is the smallest is set as the initial value (set as the median value of the detection range), and the actual measurement May be performed. This correction corresponds to Step 2 (correction processing) described later.

The overall measurement time adjustment will be described using a flowchart. FIG. 7 is a flowchart showing a processing procedure example of the measurement time adjustment processing. The measurement time adjustment process is a process performed mainly by the adjustment unit 42 of the electronic chip 4. The adjustment unit 42 performs an initial correction process (step S1). The initial correction process is a process mainly intended to correct a clock error of the electronic chip 4. The adjustment unit 42 performs correction processing (step S2). The correction process is a process mainly intended to minimize the difference in the number of measurement pulses between the first oscillation circuit 6 and the second oscillation circuit 7 in an environment assumed to be the median value of the measurement range. . The adjustment unit 42 performs a forced correction process (step S3). The forced correction process is a process for forcibly setting the difference in the number of measurement pulses between the first oscillation circuit 6 and the second oscillation circuit 7 to 0 in an environment that is assumed to be the median value of the measurement range. The forcible correction process is a process for forcibly setting the minimum value of the difference obtained in the correction process to 0, and includes the meaning of confirming that the difference has reached the minimum value in the correction process. The adjustment unit 42 ends the measurement time adjustment process.
Thereafter, eddy current measurement is repeatedly performed according to the procedure shown in FIG. 6 (step S4).

  FIG. 8 is a flowchart showing an example of the processing procedure of the initial correction process. The coil constituting the first oscillation circuit 6 is a reference coil, the coil constituting the second oscillation circuit 7 is a detection coil, the first oscillation circuit 6 is a reference oscillation circuit, and the second oscillation circuit 7 is a detection oscillation circuit. The adjustment unit 42 measures the number of oscillation pulses of the first oscillation circuit 6 with the measurement unit 41 during a predetermined initial measurement time (t0) (step S11). The adjustment unit 42 calculates the difference between the number of pulses measured by the calculation unit 43 and a predetermined value (step S12). Based on the predetermined value, the measurement time of the first oscillation circuit 6 is corrected so that the number of oscillation pulses of the first oscillation circuit 6 becomes a predetermined value (step S13). The adjustment unit 42 ends the initial correction process and returns the process to the caller. The corrected measurement time is, for example, t0 + α. In step 13, the initial correction is completed. Note that after step S13, at the measurement time t0 + α, the measurement unit 41 measures the number of oscillation pulses of the first oscillation circuit 6, and performs a process of confirming whether or not the measured number of oscillation pulses becomes a predetermined value. At the measurement time t0 + α, the number of oscillation pulses of the first oscillation circuit 6 is measured (step S14). The adjustment unit 42 determines whether or not the number of oscillation pulses has reached a predetermined value (step S15). When the adjustment unit 42 determines that the number of oscillation pulses is not the predetermined value (NO in step S15), the process returns to step S12. If the adjustment unit 42 determines that the number of oscillation pulses is a predetermined value (YES in step S15), the adjustment unit 42 ends the process and returns to the caller. When the number of oscillation pulses does not reach a predetermined value or when α does not converge, a value that minimizes the difference between the number of oscillation pulses and the predetermined value is set to α. In addition, in order to simplify a process, you may abbreviate | omit the process of step S14, S15.

  For example, the first oscillation circuit 6 is designed to oscillate at 10 MHz. The number of oscillation pulses is measured 30,000 times. In this case, the initial measurement time t0 is 3 ms. The measurement unit 41 measures the number of oscillation pulses of the first oscillation circuit 6 for 3 ms. When the measured number of oscillation pulses is less than 30,000, the measurement time is lengthened by the number of pulses below. That is, α is a positive value. When the measured number of oscillation pulses exceeds 30,000, the measurement time is shortened by the number of pulses exceeding the number. That is, α is a negative value. If the measured number of oscillation pulses is 30,000, α is set to zero.

  FIG. 9 is a flowchart illustrating an example of a processing procedure of correction processing. The correction process is performed in an environment where an eddy current at the center of the measurement range is measured. For example, a reference metal plate that creates such an environment is used. For example, when using an eddy current type metal sensor as a distance sensor, a reference metal plate made of an assumed metal is arranged at a distance desired to be the center of the measurement range. The adjustment unit 42 measures the number of oscillation pulses of the first oscillation circuit 6 by the measurement unit 41 at the measurement time t0 + α obtained in the initial correction process (step S21). The adjustment unit 42 stores the measured number of oscillation pulses of the first oscillation circuit 6 (step S22). The adjustment unit 42 measures the number of oscillation pulses of the second oscillation circuit 7 by the measurement unit 41 at the measurement time t0 + α obtained in the initial correction process (step S23). The adjustment unit 42 calculates a difference between the number of oscillation pulses of the second oscillation circuit 7 measured by the calculation unit 43 and the number of oscillation pulses stored in the first oscillation circuit 6 (step S24). The adjustment unit 42 ends the correction process and returns the process to the caller. The measurement time of the second oscillation circuit 7 is corrected so that the difference becomes 0 (step S25). The adjusting unit 42 sets the corrected measurement time to, for example, t0 + α + β. When the number of pulses of the second oscillation circuit 7 is smaller than the number of oscillation pulses of the first oscillation circuit 6, β is set to a positive value. When the number of pulses of the second oscillation circuit 7 is larger than the number of oscillation pulses of the first oscillation circuit 6, β is set to a negative value. When the number of pulses of the second oscillation circuit 7 is equal to the number of oscillation pulses of the first oscillation circuit 6, β is set to zero. After step S25, the number of oscillation pulses of the first oscillation circuit 6 is measured at the measurement time t0 + α, the number of pulses of the second oscillation circuit 7 is measured at the measurement time t0 + α + β, and it is confirmed whether or not both pulses are equal. May be performed. If they are not equal, β is set again. If β does not converge, the difference between the number of oscillation pulses and the predetermined value is set to the smallest value. Specifically, after step S <b> 25, the adjustment unit 42 determines whether the measured number of oscillation pulses of the first oscillation circuit 6 matches the number of pulses of the second oscillation circuit 7. If the adjustment unit 42 determines that the number of pulses is the same, the adjustment process ends. If it is determined that the number of pulses does not match, the adjustment unit 42 returns to S21 and repeats step S21 and subsequent steps. The measurement time at this time is t0 + α in the first oscillation circuit 6 (step S21), and t0 + α + β in the second oscillation circuit 7 (step S23). In the same manner, the time of the second oscillation circuit 7 is corrected and the number of oscillation pulses is corrected to be the same. Further, instead of correcting the measurement time of the second oscillation circuit 7, the measurement time of the first oscillation circuit 6 may be corrected.

  FIG. 10 is a flowchart illustrating an example of a processing procedure for forced correction processing. The forcible correction process is a process for finally checking the difference in the number of oscillation pulses at the measurement time set in the correction process and forcing the difference to zero. Similar to the correction process, the forced correction process is performed in an environment where an eddy current at the center of the measurement range is measured using a reference metal plate. The adjustment unit 42 measures the number of oscillation pulses of the first oscillation circuit 6 by the measurement unit 41 at t0 + α (step S31). The adjustment unit 42 stores the measured number of oscillation pulses of the first oscillation circuit 6 (step S32). The adjustment unit 42 measures the number of oscillation pulses of the second oscillation circuit 7 by the measurement unit 41 at t0 + α + β (step S33). The adjustment unit 42 stores the measured number of oscillation pulses of the second oscillation circuit 7 (step S34). The adjustment unit 42 uses the calculation unit 43 to calculate the difference between the number of oscillation pulses of the first oscillation circuit 6 and the number of oscillation pulses of the second oscillation circuit 7 (step S35). Thereafter, the difference is forcibly set to 0. With this process, the value measured with the reference metal plate is set as the median value of the eddy current (step S36). This process shows S52 to S57 described later.

  A series of correction processing (forced correction after correction) will be described with reference to a flowchart. FIG. 11 is a flowchart illustrating an example of a forced correction process procedure after the correction process is corrected. The adjustment unit 42 sets the measurement time (first measurement time t1) of the first oscillation circuit 6 to t0 + α. The adjustment unit 42 sets the measurement time (second measurement time t2) of the second oscillation circuit 7 to t0 + α + β (step S51). The measurement unit 41 measures the number of oscillation pulses of the first oscillation circuit 6 at the first measurement time t1 (step S52). The measuring unit 41 stores the measured number of oscillation pulses of the first oscillation circuit 6 (step S53). The measurement unit 41 measures the number of oscillation pulses of the second oscillation circuit 7 at the second measurement time t2 (step S54). The measuring unit 41 stores the measured number of oscillation pulses of the second oscillation circuit 7 (step S55). The adjustment unit 42 corrects the number of oscillation pulses of the first oscillation circuit 6 or the number of oscillation pulses of the second oscillation circuit 7 with the difference (forced difference) obtained in the forced correction process. In the forced correction process, when the number of oscillation pulses of the first oscillation circuit 6 is larger than the number of oscillation pulses of the second oscillation circuit 7, the forced difference is added to the value of the number of oscillation pulses of the second oscillation circuit 7. When the number of oscillation pulses of the first oscillation circuit 6 is smaller than the number of oscillation pulses of the second oscillation circuit 7, a forced difference is subtracted from the value of the number of oscillation pulses of the second oscillation circuit 7 (the difference is forcibly set to 0). This completes the correction (steps S56 and S57). By this processing, the measured value at the reference metal plate is set as the median value of the eddy current.

By performing the adjustment as described above, fluctuations in the detection output due to temperature fluctuations can be suppressed. In addition, compensation for the difference in characteristics between the first coil 1 and the second coil 2 during the formation as described above can be performed as a result. Therefore, in the eddy current type metal sensor 20 of the present embodiment, it is possible to detect the eddy current with high accuracy while suppressing the influence of temperature fluctuation.
The initial correction in step S1 and the forced correction in step S3 are not essential, and may be combined as appropriate according to the required specifications.
When the correction and the forced correction are performed after the initial correction, the measurement time of the reference coil (first coil 1 in this specification) is constant and the measurement time of the detection coil (second coil 2 in this specification). It is desirable to adjust.

  In the embodiment described above, the change in inductance of the two coils (the first coil 1 and the second coil 2) coaxially arranged on the substrate 10 is measured with the accuracy of the oscillator built in the microcomputer (electronic chip 4). Is detected as the difference in the number of oscillation pulses in the 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 the number of oscillation pulses) is calculated by a microcomputer Processing to detect changes in eddy currents. Here, each of the two coils is alternately connected to the oscillation circuit, and the number of oscillation pulses is alternately measured over a predetermined time by a microcomputer, and the difference is calculated to detect a change in eddy current. ing.

  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 number of oscillation pulses in the two oscillation circuits is performed alternately, the measurement of the oscillation circuit including one coil is affected by the magnetic flux generated in the other coil (inductance change in the other coil). Therefore, the exact number of oscillation pulses 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. 12 is a cross-sectional view showing the configuration of the eddy current metal sensor in the first modification. In FIG. 12, 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.

(Second modification)
FIG. 13 is a cross-sectional view illustrating a configuration of an eddy current metal sensor according to a second modification. 13, 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 an air coil as a separate component on the upper surface of one end portion of the substrate 10, and is coaxial with the first coil 1 on the lower 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. 14 is a cross-sectional view showing a configuration of an eddy current metal sensor according to a third modification. 14, 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. Two air-core coils are laminated on the substrate in the order of the second coil 2 and the first coil 1. An insulating layer is provided between the second coil 2 and the first coil 1. 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. 13, 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.

  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 Adjustment unit 43 Calculation unit 44 Conversion unit

Claims (14)

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 the number of oscillation pulses in each of the first oscillation circuit and the second oscillation circuit;
An adjustment unit that adjusts at least one of a measurement time of the number of oscillation pulses in the first oscillation circuit by the measurement unit and a measurement time of the number of oscillation pulses in the second oscillation circuit by the measurement unit;
A calculation unit for calculating a difference in the number of pulses 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 according to claim 1, wherein the measurement unit is configured to alternately measure the number of oscillation pulses in the first oscillation circuit and the number of oscillation pulses in the second oscillation circuit. Metal sensor.   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,
Arranging a coil assembly including a first coil and a second coil having different distances from the object to be detected;
Measuring the number of oscillation pulses of the first oscillation circuit that oscillates including the first coil and the number of oscillation pulses of the second oscillation circuit that oscillates including the second coil;
Adjusting at least one of a first measurement time for measuring the number of oscillation pulses of the first oscillation circuit and a second measurement time for measuring the number of oscillation pulses of the second oscillation circuit;
Calculate the difference in the number of measured oscillation pulses,
An eddy current detection method comprising converting the calculated difference into an eddy current of the object to be detected.   When the distance from the object to be detected of the second coil is shorter than the distance from the object to be detected of the first coil, the second measurement time is relatively longer than the first measurement time. The eddy current detection method according to claim 6, wherein at least one of the first measurement time and the second measurement time is adjusted. In an eddy current type metal sensor that detects eddy currents of metal objects,
A first oscillation circuit that oscillates including a first coil whose inductance changes due to eddy current of the object to be detected;
A second oscillation circuit that oscillates including a second coil whose inductance changes due to the eddy current of the object to be detected;
A measurement unit for measuring the number of oscillation pulses in each of the first oscillation circuit and the second oscillation circuit;
A first adjustment unit for adjusting a measurement time so that the number of oscillation pulses in the first oscillation circuit by the measurement unit becomes a predetermined value;
At least one of the measurement time of the number of oscillation pulses in the first oscillation circuit adjusted by the first adjustment unit and the measurement time of the number of oscillation pulses in the second oscillation circuit is measured under a predetermined environment. A second adjustment unit for adjusting based on the number of oscillation pulses;
A calculation unit that calculates a difference in the number of oscillation pulses measured by the measurement unit in a measurement time after adjustment by the first adjustment unit and the second adjustment 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.   The eddy current metal sensor according to claim 8, wherein the second adjustment unit adjusts a measurement time of the number of oscillation pulses in the second oscillation circuit. After the adjustment of the measurement time by the first adjustment unit and the second adjustment unit, the calculation unit, after the adjustment by the first adjustment unit and the second adjustment unit, in the measurement unit under a predetermined environment Calculate the difference in the number of oscillation pulses measured at the measurement time,
The third adjustment unit that adjusts at least one of the number of oscillation pulses in the first oscillation circuit and the number of oscillation pulses in the second oscillation circuit based on the difference calculated by the calculation unit. The eddy current type metal sensor according to claim 8 or 9.   The eddy current metal sensor according to claim 10, wherein the third adjustment unit adjusts the number of oscillation pulses in the second oscillation circuit. The eddy current metal sensor according to any one of claims 8 to 11, wherein the predetermined environment is realized using a reference metal plate. In an eddy current detection method for detecting an eddy current of a metal object,
Arrange the coil assembly in which the detection coil and the reference coil are coaxial, or the axes of each other are parallel and overlap in the axial direction.
Measure the number of oscillation pulses of a reference oscillation circuit that oscillates including the reference coil at a predetermined initial measurement time,
Obtaining a first measurement time obtained by adjusting the initial measurement time so that the measured number of oscillation pulses becomes a predetermined value;
After setting the same time as the obtained first measurement time as the second measurement time, and arranging the reference metal plate at a predetermined position near the detection coil,
Measure the number of oscillation pulses of the reference oscillation circuit in the first measurement time and the number of oscillation pulses of the detection oscillation circuit that oscillates including the detection coil in the second measurement time,
Adjusting at least one of the first measurement time and the second measurement time based on the measured two oscillation pulse numbers;
In an environment where the reference metal plate is removed and the object to be detected is present, the number of oscillation pulses of the reference oscillation circuit at the first measurement time and the number of oscillation pulses of the detection oscillation circuit at the second measurement time, respectively. Measure and
Calculate the difference in the number of measured oscillation pulses,
An eddy current detection method comprising converting the calculated difference into an eddy current of the object to be detected.   The eddy current detection method according to claim 13, wherein the second measurement time is adjusted.

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