JP5047833B2 - Displacement sensor system and displacement sensor - Google Patents

Description

  The present invention relates to a distance measurement sensor system for detecting a distance and a position with respect to a measurement object and a displacement sensor used in the system.

  As a distance measuring method for measuring the distance to a measurement object having conductivity such as metal in a non-contact manner, two methods are roughly classified. That is, (1) A method of detecting a slight electric loss due to an eddy current loss in an oscillation circuit and detecting a displacement; (2) A displacement is minutely detected by detecting a change in L or C in an LC oscillation circuit. A method of calculating as a change in voltage or current has been proposed. FIG. 1 shows an outline of a displacement sensor using the method (2). The eddy current displacement sensor generates a high frequency magnetic field by flowing a high frequency current through a three-dimensional winding (coil) built in the sensor head 10. An eddy current in a direction perpendicular to the passage of magnetic flux flows through the surface of the object to be measured placed in the magnetic field by the electromagnetic induction action, and the impedance of the sensor coil changes. Due to this change in impedance, an oscillation waveform as shown in FIG. 2 is obtained. As the distance between the object to be measured and the sensor head 10 decreases, the eddy current increases and the oscillation amplitude decreases as shown in FIG. The oscillation amplitude is rectified to change the DC voltage. As described above, the eddy current displacement sensor detects the change in the oscillation state by the amplitude and measures the distance.

However, in this method, the accuracy of distance measurement depends on the detection accuracy of the amplitude of the rectified waveform obtained by rectifying the oscillation waveform. For this reason, there is a problem that the smaller the amplitude waveform is, the more difficult it is to detect the amount of change, and it is difficult to improve the measurement accuracy. Currently, several hundred KHz to several MHz are used as the oscillation frequency, and in order to achieve high performance, a method of increasing a small change or a small amplitude as an amplifier function for enlarging a small amplitude change. There are two possible functions for finely decomposing changes: a method of finely degrading minute changes. The former method requires a high-performance amplifier with a low S / N ratio in order to amplify the amplitude. The latter method also requires a high resolution A / D converter with a low S / N ratio. Such a high-performance analog device with a low S / N ratio is very expensive and generally requires several hundred thousand to several million yen, and its realization has not been easy. In particular, in recent years, while higher speed and higher accuracy are required, a simpler and cheaper displacement sensor is required, and a displacement sensor that can meet these requirements is strongly desired.
Japanese Patent No. 3352619

  The present invention has been made to solve such conventional problems. A main object of the present invention is to provide a displacement sensor system and a displacement sensor that can realize distance measurement with extremely high accuracy at low cost.

Means for Solving the Problems and Effects of the Invention

In order to achieve the above object, according to the first displacement sensor system of the present invention, a displacement sensor system capable of measuring the distance between the object to be measured in a non-contact manner, including a planar coil, It is possible to detect a state in which the oscillation frequency of the oscillation circuit changes according to the distance between the oscillation circuit electrically connected to the planar coil and the measurement object close to the planar coil and the planar coil. A frequency detection means, a digital output means capable of outputting the oscillation frequency detected by the frequency detection means as a digital signal, a time control means capable of controlling a detection operation time for detecting the oscillation frequency by the frequency detection means, and a time A controller having an operation time instruction means capable of sending a control signal instructing a detection operation time to the control means, and an oscillation frequency detected by the frequency detection means A frequency type displacement sensor system that calculates a change in distance between a measurement object and the planar coil based on the calculation result, and that can output the calculation result as a digital value by the digital output means. The detection operation time can be made variable according to the response time until the distance measurement result is obtained. Thereby, the detection operation time such as the integration time can be made variable by the control signal from the outside of the displacement sensor, and the measurement accuracy and the response speed of the measurement result can be adjusted to desired values. Further, according to the displacement sensor system, the frequency detection means is constituted by a frequency counter capable of counting and integrating the oscillation frequency, and the operation time instruction means can be configured to control the integration time of the frequency counter. Further, the frequency counter is configured to calculate a distance measurement result after continuously performing frequency counting a plurality of times, and the frequency counter and the digital output means can be a packaged IC. This makes it possible to calculate the integrated value of the oscillation frequency by repeating the distance measurement operation, and the distance measurement result can be calculated after continuously performing frequency counting a plurality of times. Compared to the above, it is possible to realize extremely accurate distance measurement with reduced effects of noise and errors. Further, as a miniaturized IC, it can be thinned so that it can be placed in a narrow place.

Further, according to the second displacement sensor system, the frequency counter is controlled by the rectangular wave input from the operation time instruction means, the frequency counter is reset at the rising edge of the rectangular wave, and at the falling edge. The count operation is held, and the count value accumulated up to that point can be output as serial data. As a result, the measurement range can be dynamically switched.

Furthermore, according to the third displacement sensor system, the oscillation frequency of the oscillation circuit can be 30 MHz or more. By using the high frequency band in this way, the distance measurement resolution can be remarkably improved, and the inductance of the planar coil can be kept low, so there is no need to make the coil three-dimensional, making it thinner and smaller. Therefore, it is possible to realize a compact displacement sensor system that can be installed even in a small space.

Furthermore, according to the fourth displacement sensor system, the planar coil can be a round or square spiral coil.

Furthermore, according to the fifth displacement sensor system, the oscillation circuit, the frequency detection means, and the digital output means are mounted on the same substrate to constitute a sensor body, and the planar coil protrudes from the sensor body. A sensor head can be configured. As a result, the detection operation time can be controlled by changing only the sensor body, and the planar coil can be shared, so that the measurement accuracy and response time can be adjusted using the existing planar coil. Is possible.

Furthermore, according to another displacement sensor, in the displacement sensor capable of measuring the distance between the measurement object in a non-contact manner, a planar coil, an oscillation circuit electrically connected to the planar coil, A change in the oscillation frequency of the oscillation circuit is detected by counting and integrating the oscillation frequency of 30 MHz or more according to the distance between the measurement object close to the planar coil and the planar coil. A frequency counter capable of outputting a digital value; a digital output means capable of outputting the oscillation frequency detected by the frequency counter as a digital signal; and a time control means capable of controlling an integration time for detecting the oscillation frequency by the frequency counter. And calculating a change in distance between the object to be measured and the planar coil based on the oscillation frequency detected by the frequency counter, and calculating the result of the calculation It can be output as a digital value by the Le output means. Thereby, the integration time can be varied by a control signal from the outside of the displacement sensor, and the measurement accuracy and the response speed of the measurement result can be adjusted to desired values. In particular, it is possible to calculate the integrated value of the oscillation frequency by repeating the distance measurement operation, and the distance measurement result can be calculated after the frequency counter continuously counts the frequency a plurality of times. Compared with measurement, it is possible to realize extremely high-precision distance measurement with reduced effects of noise and errors. Further, according to the displacement sensor, the frequency counter and the digital output means can be configured by a packaged IC. As a result, as a miniaturized IC, it can be thinned so that it can be placed in a narrow place.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a displacement sensor system and a displacement sensor for embodying the technical idea of the present invention, and the present invention specifies the displacement sensor system and the displacement sensor as follows. do not do. Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the constituent members described in the embodiments are not intended to limit the scope of the present invention only to the description unless otherwise specified. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing. In addition, the contents described in some examples and embodiments may be used in other examples and embodiments.

  The configuration of the displacement sensor system 100 according to the embodiment of the present invention is shown in the block diagram of FIG. A displacement sensor 100 shown in this figure includes a sensor head 10 and a sensor body 20. The sensor head 10 constitutes an oscillation circuit, the frequency detection means 22 for detecting a change in the oscillation frequency of the oscillation circuit according to the distance from the object to be measured WK, and the oscillation frequency detected by the frequency detection means 22 as a digital signal. Digital output means 24 capable of outputting as a signal. The frequency detection means 22 has time control means 23 for controlling the detection operation time for detecting the oscillation frequency, and the detection operation time is controlled by the controller 30. For this reason, the controller 30 is provided with an operation time instruction means 31 for sending a control signal instructing the detection operation time to the time control means 23.

  The oscillation circuit is connected to the planar coil 1. The planar coil 1 is provided on the surface of the sensor head 10, and the sensor head 10 is fixed so that the planar coil 1 is in a posture facing the measuring object WK. This displacement sensor system 100 calculates the distance from the object to be measured WK from the change in the oscillation frequency determined by the LC of the oscillation circuit, and measures it without contact. For example, the planar coil 1 is provided on the back surface side of the protruding substrate, and the oscillation circuit is disposed on the front surface side of the protruding substrate. Further, the sensor head 10 can be miniaturized by mounting a member such as a frequency counter on the substrate as a dedicated IC. The sensor head can be used as a single displacement sensor by providing a planar coil on a substrate as described later and arranging a dedicated IC on the back surface.

  The displacement sensor having this configuration does not calculate the distance between the coil and the object to be measured based on the amplitude of the oscillation waveform of the current or voltage as in the prior art, but measures the distance between the planar coil 1 and the measurement based on the change in the oscillation frequency. Calculate the distance to the object. Such a frequency system has the advantage that it is excellent in noise resistance and easy to achieve high accuracy as compared with the conventional amplitude system. That is, more accurate measurement is possible by counting the frequency than the method of capturing a simple voltage change, and the S / N ratio and the reliability are excellent. Further, while the rectifier circuit can be eliminated, the oscillation frequency can be easily detected by the frequency detection means 22 such as a frequency counter, and since it is suitable for digital processing, a member such as a high resolution A / D converter can be dispensed with. .

  Furthermore, by increasing the oscillation frequency, the inductance of the coil can be reduced, and the coil itself can be reduced in size. In particular, the two-dimensional coil can be used without winding the coil three-dimensionally, and the planar coil 1 is advantageous for thinning. The oscillation frequency is preferably 30 MHz or more, for example, 100 MHz to 1 THz, more preferably 100 MHz to 500 MHz.

  As a comparative example, comparing the case where the conventional frequency integration method is performed at 300 kHz and the case where the frequency integration method is performed at 300 MHz (300000 kHz) according to the present embodiment, when the measurement time is 200 μs, the integrated count value of the frequency counter (CNT) is 60CNT in the conventional example and 60000 in the present embodiment, and the resolution can be improved by 1000 times when the same time measurement is performed. Further, if the same resolution is to be realized in the conventional example, the measurement time is 200 ms, which is 1000 times longer.

  In addition, the frequency detection means 22 can obtain the accumulated oscillation frequency. For this reason, the oscillation frequency can be calculated as an average value or the like after continuously detecting the oscillation frequency a plurality of times. This, combined with the fact that the oscillation frequency can be increased, can make the detection accuracy extremely high. In other words, since the oscillation frequency is high, the time required for one frequency detection operation can be shortened. As a result, continuous oscillation frequency detection operation is possible, and the sudden effect such as noise is reduced from the average value. Accurate and reliable distance measurement can be realized.

  For example, if the frequency integration method is performed for 200 μs at an oscillation frequency of 300 kHz with a conventional displacement sensor, the integration count value is 60, and if the measurement of 200 μs is performed at 300 MHz according to the present embodiment, the integration is performed. The count value can be 60000, and the resolution can be improved 1000 times. If a similar resolution is to be realized at the conventional oscillation frequency of 300 kHz, a time that is 1000 times 200 μs and 200 ms are required. Thus, when measuring for the same time, the accuracy can be increased as the oscillation frequency is increased.

  On the other hand, if the measurement is to be obtained with the same degree of accuracy, the processing can be completed in a shorter time as the oscillation frequency is higher. For this reason, this embodiment is also suitable for applications in which response speed is more important than accuracy. In the conventional displacement sensor, since the measurement accuracy and the response speed are fixed, it is necessary to redesign the sensor according to the application and specifications. In particular, in the field of displacement sensors in recent years, higher speed and higher resolution are demanded, but it is not easy to meet these requirements within the limits of limited manufacturing cost and lead time. In contrast, the present embodiment has an excellent feature that the detection accuracy and response speed can be changed very easily. Since the detection accuracy and the response speed are in a trade-off relationship, the user can set an appropriate detection accuracy and response speed according to the application. In order to realize this, in the present embodiment, time control means 23 for controlling the oscillation frequency detection operation is provided as shown in FIG. When the ON signal is input to the time control means 23, the oscillation frequency detection operation is executed, and when the OFF signal is input, the detection operation is stopped. Therefore, by changing the control signal so as to obtain a desired detection operation time, it is possible to define the calculation time, that is, the response speed necessary for obtaining the distance measurement result. In addition, the distance can be measured with higher accuracy by increasing the calculation time. In particular, in this embodiment, since the oscillation frequency is calculated by integrating with the frequency counter, highly reliable distance measurement with high reliability is realized by repeatedly measuring the distance and calculating the average value. Thus, the displacement sensor according to the present embodiment can be easily adjusted to a desired accuracy and response speed.

  The planar coil 1 connected to the oscillation circuit 76 measures the oscillation frequency by the oscillation circuit 76 when there is a conductive member (a conductor such as an opposing metal) that is a measurement object WK that is close to the planar coil 1. Thus, the distance between the planar coil 1 and the conductive member or the change in distance can be calculated. Here, displacement detection based on electrostatic coupling will be described. In electrostatic coupling distributed inductance type displacement detection, an inductor for measuring a distance and a conductor are electrostatically coupled. In order to maximize the electrostatic coupling, the inductor for measuring the distance has a two-dimensional structure. When a conductor is brought close to a two-dimensionally distributed planar inductor, the electrostatic coupling is maximized, so that the sensitivity of the planar inductor for measuring the distance is increased and the power consumption is minimized. When the two-dimensionally distributed planar inductor and the conductor are electrostatically coupled, the conductor and conductor of the two-dimensionally distributed planar inductor are equivalently capacitors. That is, the conductor portion of the planar inductor distributed two-dimensionally becomes one electrode of the distributed capacitor, and the other electrode becomes a conductor. In general, as the frequency of the current flowing through the circuit increases, the current flowing through the capacitor increases, but the current flowing through the planar inductor decreases. When the distance between the two-dimensionally distributed planar inductor and the conductor is shortened, the capacitance of the distributed capacitor increases, so that the inductance of the two-dimensionally distributed planar inductor is equivalently reduced. That is, since the inductance decreases, the frequency of the current flowing through the oscillation circuit 76 increases. Therefore, if a change in frequency is detected, it is possible to measure a change in the distance between the planar inductor distributed in a two-dimensional manner and the conductor.

  A circuit diagram of the displacement sensor is shown in FIG. In this displacement sensor, the oscillation circuit is composed of an LC oscillation circuit in which an oscillation coil L1 and a capacitor C1 are connected in series, and a CMOS inverter (for oscillation) 72 and (for buffer) 73 are connected. The oscillation circuit oscillates at a high frequency, and an induced current due to electromagnetic induction is generated on the surface of the conductor by the magnetic field generated from the oscillation coil L1, and is consumed as electromagnetic energy. When the conductor moves and approaches the oscillation coil L1, the oscillation frequency changes in the oscillation circuit. In the example of FIG. 4, the resistance component R1 of the circuit itself is present on the input side of the CMOS inverter (for oscillation) 72, but a resistor can be added separately. In addition, the capacitor C1 connected to the input side can be replaced with another capacitor in addition to a fixed type. In particular, by using the capacitor C1 as a variable capacitor, it is possible to adjust the oscillation frequency of the LC oscillation circuit, and it is possible to eliminate the mismatch of the oscillation frequencies caused by the variation in the characteristics of the elements for each device. Furthermore, by feeding back the output side of the CMOS inverter (for oscillation) 72, the output can be stabilized by feedback control.

  Next, FIG. 5 shows a block diagram of a detection system that detects a displacement amount with a displacement sensor. This block diagram includes an oscillation circuit 76, a frequency counter 77, a buffer circuit 78, and a control circuit 79. These can be constituted by dedicated ICs. When pressure is applied to the detection target and the detection target surface moves, the frequency f of the oscillation circuit 76 built in the displacement sensor changes. The frequency counter 77 is used to measure the frequency f and the measurement data is stored in the buffer circuit 78. The frequency counter 77 and the buffer circuit 78 are controlled by the control circuit 79. By reading the data stored in the buffer circuit 78, the displacement can be measured. Further, a stabilized power supply circuit 80 that stabilizes the driving power can be added as necessary. In the circuit example of FIG. 5, the modulation circuit that modulates the output of the frequency counter is not provided, and the result of the frequency counter is directly output, thereby simplifying the circuit and reducing the processing. However, it is also possible to modulate and transmit by providing a modulation circuit or the like.

  The principle of operation of this displacement sensor will be described based on the block diagram of FIG. This figure shows a conductor as a displacement measurement object WK, a sensor IC 95 constituting a displacement sensor, and a display unit 98 for displaying a measurement result. In the displacement sensor, the sensor IC 95 is opposed to the conductor to generate a distributed capacitance with the distributed inductance, thereby forming an LC oscillation circuit, and the oscillation frequency is measured by the frequency counter of the sensor IC 95. The sensor IC 95 outputs the count value of the frequency counter as a digital signal to the display unit 98, and the display unit 98 converts it into a unit of length and displays it. The digital circuit that counts with the frequency counter can be realized with a simple configuration. A conventional amplifier can be dispensed with. In particular, with analog sensors, measurement values are measured instantaneously. Therefore, high-resolution amplifiers with high resolution are required to detect instantaneously obtained data with high accuracy, which increases costs. . On the other hand, since the counter is inexpensive and is processed by cumulative counting, the resolution can be improved by increasing the sampling time. As a result, highly accurate measurement is realized using an extremely inexpensive circuit. In addition, a high-performance displacement sensor that can cope with a rotational speed of 20,000 revolutions or more can be realized without problems such as drift that can be a problem with analog circuits. Furthermore, since processing with a digital signal can be performed, an A / D converter or the like is not required, and output directly to a computer or the like is possible. For the sensor IC 95, a downsized type such as a chip size package can be suitably used. As shown in FIG. 2, the oscillation frequency of the oscillation circuit 76 changes according to the distance between the opposing conductor such as a metal and the sensor IC 95. In particular, as indicated by A in FIG. 2, since the change in the oscillation frequency is large in the range of 0 mm to 1 mm, if this region is used, measurement with extremely high resolution and high accuracy becomes possible. This method is similar to the eddy current method, but the resolution can be greatly improved by using a high frequency band. In particular, since the oscillation frequency can be used in a high order of several tens of MHz to several hundreds of MHz, the displacement can be measured with high accuracy without being substantially affected by the thickness of the opposing conductive member. Furthermore, the circuit can be miniaturized and can be driven with low power consumption.

The above-described capacitively coupled distributed inductance type displacement sensor has a high spatial resolution and can be instantaneously measured even in the order of μm to nm, and is suitable for real-time processing. In addition, A / D conversion is unnecessary because digital output is obtained. Is obtained. In the above embodiment, an electrostatic coupling distributed inductance type displacement sensor is used as the displacement sensor. For such a displacement sensor, a distance measuring IC previously developed by the present applicant can be used. Details of the distance measuring IC are described in Patent Document 2, and therefore detailed description thereof is omitted. However, as a displacement sensor using other methods, for example, a laser light displacement sensor, a capacitive displacement sensor, an eddy current displacement sensor, or the like can be used. In this manner, by integrating the counter substrate into the sensor IC, the displacement sensor can be further reduced in size and power consumption.
(Planar coil 1)

  The planar coil 1 is preferably arranged so as to be exposed from the sensor head 10. For example, when the sensor head 10 is configured by mounting a component such as an IC on a substrate, the planar coil 1 is provided on the back side of the mounting surface of the substrate. Further, the surface of the planar coil 1 is preferably covered with a protective film to prevent external contamination and oxidation. In this sense, the expression does not necessarily mean that the planar coil 1 is exposed, but includes an example in which the planar coil 1 is disposed near the surface of the sensor head 10.

  In the above example, a square spiral coil is used as the planar coil 1. FIG. 6A shows a plan view of the square spiral coil 2, and FIG. 6B shows a cross-sectional view of the square spiral coil 2. The rectangular spiral coil 2 has an advantage that it can be easily arranged at a high density in a rectangular region and has a high mounting density. However, the present invention is not limited to a square coil, and it is also possible to use a round spiral coil 4 as shown in FIG. FIG. 7B shows a cross-sectional view of the round spiral coil 4. The round spiral coil 4 has a feature that position detection can be performed with high accuracy. These planar coils 1 are simple in structure and can be advantageously reduced in size.

  In order to increase the resolution, it is desired to reduce the size of the coil and increase the number of windings so that the coil is effectively arranged in a limited area. However, if the coil is to be miniaturized, the coil wire width becomes narrower and the number of turns decreases, making the manufacturing complicated and the accuracy tending to decrease. Therefore, in order to secure the number of turns while measuring the miniaturization of the coil, in this embodiment, a configuration in which the coil is multilayered as shown in FIGS. 8 and 9 can be adopted. In FIG. 8A, the rectangular spiral coil 3 has a two-layer structure, and the coils are arranged in an offset manner in the upper and lower layers as shown in FIG. 8B. Thereby, the number of turns can be substantially increased while maintaining the line width of the coil. The wider the line width (pattern width) of the coil, the smaller the resistance of the coil and the more stable the oscillation, and the more accurate detection becomes possible. Similar advantages can be obtained with the two-layer structure of the round spiral coil 5 shown in FIGS. 9 (a) and 9 (b).

Such a two-layer structure can be easily realized by using a multilayer substrate such as a double-sided substrate or a laminated substrate as the substrate on which the coil pattern is formed. The upper and lower coil layers can be connected through a through hole or the like. Since the planar coil 1 is extremely thin, the number of turns can be increased without increasing the substantial thickness of the double-sided substrate. In this way, it is possible to measure the high performance by reducing the size of the coil and increasing the number of turns.
(Controller 30)

As described above, the detection operation time is controlled by the control signal input to the time control means 23. On the controller 30 side, an operation time instruction means 31 for sending a control signal is provided. Further, the controller 30 may have a function of calculating a distance based on the oscillation frequency counted by the frequency counter.
(Sensor head 10)

  FIG. 10 shows an external perspective view of the displacement sensor system 100. A displacement sensor system 100 shown in this figure includes a sensor head 10 and a sensor body 20. The sensor head 10 is a protruding substrate including the planar coil 1, and is fixed in a posture protruding from the end surface of the sensor main body 20 in an orthogonal posture through the lead 12. The sensor head 10 is electrically and mechanically fixed to the sensor body 20 by soldering or the like. Therefore, by selecting the sensor head 10 including the planar coil 1 having an appropriate size and shape according to the size of the measurement object WK at the time of manufacture, an optimal displacement sensor system according to the purpose and application can be obtained. realizable. The sensor head may be detachable from the sensor body 20.

  The sensor head 10 can perform more stable measurement by increasing the parallelism with the measurement object WK that faces the sensor head 10. Therefore, when installing the displacement sensor system, precise positioning is performed so that the object to be measured WK and the sensor head 10 are kept parallel. Further, in relation to this, stable measurement can be performed by increasing the surface accuracy of the sensor head 10 itself or the opposing measuring object WK (opposing metal).

The amount of change in the L (inductor) component of the LC oscillation circuit greatly contributes to the performance of the displacement sensor. As the conductor that is the measurement object WK that faces the L component of the spiral coil that is the planar coil 1 approaches, the capacitance of the distributed inductor is reduced as shown in FIG. The oscillation frequency f at this time can be expressed by f = 1 / 2π√LC. Here, in order to increase the amount of change of L, it is preferable to use a planar coil 1 having higher conductivity. As the material of the coil, Ag is most preferable, and Cu, gold, and the like can be suitably used. As a result, high performance of the sensor can be realized. Further, the material of the counter metal also has a larger amount of change of L as the conductivity is higher as in the planar coil 1, and measurement with high resolution becomes possible. If the counter metal is larger than the sensor head 10, the maximum change can be obtained. On the other hand, if the counter metal is smaller than the sensor head 10, resolution or responsiveness is sacrificed in proportion to the size. Therefore, it is preferable to select the sensor head 10 having an appropriate size and shape according to the size of the measurement object WK.
(Sensor body 20)

  The sensor body 20 has a sensor IC 95 in which the frequency counter and the digital output means 24 are integrated, mounted on a substrate. Furthermore, the oscillation circuit may be integrated into the same IC. The displacement sensor system configured as described above is excellent in convenience because the sensor operation can be controlled by changing only the sensor main body using an existing planar coil with a common sensor head portion.

  In addition to the configuration in which the sensor head 10 and the sensor main body 20 are separated as shown in FIG. 10, the planar coil 1 is mounted on one surface of the substrate 14 and the IC is mounted on the opposite back side as shown in FIG. The displacement sensor can be collected on the single substrate 14. Thereby, as a thin displacement sensor in which the planar coil 1 is integrated, a high-performance small displacement sensor that can be arranged in a narrow place can be realized.

  In addition to the 0.5 μm CMOS process, the sensor IC 95 preferably uses a 0.35 μm CMOS process in order to achieve faster response. Further, if the wiring in the CMOS is changed from automatic wiring to manual wiring, the LC oscillation circuit connection portion that requires the most responsiveness can be minimized. In this way, the operating frequency can be improved from 300 MHz to 570 MHz, and high-speed response is realized.

  On the other hand, in order to reduce C (capacitor) which is a parasitic component of the LC oscillation circuit, it is preferable to suppress the output current value of the inverter used in the oscillation circuit. By reducing the C component in this way, it contributes to faster response.

Further, the integration circuit of the sensor IC 95 has a higher performance as the number of bits increases. For example, in the case of 17 bits, it is possible to express 131071 steps with 2 ¹⁷ , but by setting 32 bits, it becomes 2 ³² and can express 4294967295 steps, which is 32768 times the resolution of 17 bits. It can be improved.

As a comparative example, when a conventional 17-bit sensor IC 95 is used, the measurement upper limit is 200 μm, the minimum resolution is 9 nm / CNT, and the maximum resolution is 3 nm / CNT at a measurement time of 0.4 ms. At a time of 10 ms, the measurement upper limit is 1000 μm, the minimum resolution is 5 nm / CNT, and the maximum resolution is 0.11 nm / CNT. That is, according to the present embodiment, if measurement of 10 ms is performed, ultra-high-precision measurement with a resolution of about 0.1 nm, which is the hydrogen atom size, can be realized in the closest measurement of 10 μm or less. If the measurement time is further increased, the resolution can be detected more finely in proportion to this. For example, if the measurement time is 1 second, the resolution will be 1.1 × 10 ⁻³ nm, and if it is extended to 17 minutes, the resolution will be 1 fm, and measurements up to the same level as electrons and neutrons can be realized.

  The substrate material constituting the sensor head 10 and the sensor body 20 is preferably a ceramic substrate in addition to a general glass epoxy substrate. Since the expansion coefficient of the ceramic substrate is smaller than that of the glass epoxy substrate, the influence of the sensing portion on the flat coil is reduced. As a result, the sensor is stabilized and more reliable measurement is possible.

  Further, in the above configuration, the exchange of the analog signal is only between the planar coil 1 and the sensor IC 95, and the exchange is a digital signal with the outside. Therefore, since the analog signal system is closed inside the sensor, a high S / N that is resistant to noise from the outside can be realized, and in this respect also, a highly reliable high-performance displacement sensor can be realized.

Thus, in order to increase the measurement accuracy with a conventional displacement sensor using a planar coil, it was necessary to use a high-precision and expensive A / D converter or amplifier. While having such a member unnecessary, it has an extremely excellent feature that a highly accurate measurement result can be obtained with a digital signal only by a substrate on which the sensor IC 95 and the coil are mounted.
(Example)

  Next, as a specific configuration example of the displacement sensor, FIG. 12 is a block diagram of the sensor IC 95, and FIG. 13 is a timing chart. A sensor IC 95 shown in FIG. 12 includes a counter circuit 22A constituting a frequency counter, a parallel output circuit 24A and a serial output circuit 24B constituting a digital output means 24. By providing such a digital output means 24, it is possible to connect to a PLC, a PC, or the like as it is without separately preparing an amplifier and an A / D converter.

  The sensor IC 95 includes a plurality of external terminals, and constitutes connection terminals for the sensor head 10 at OUT11 and IN11. The sensor IC 95 includes two sets of oscillation circuits, and allows two systems of inputs. Here, the sensor head 10 can also be connected to OUT12 and IN12. These output side terminals OUT11 and 12 are connected to the counter circuit 22A via the buffer, and the input side terminals IN11 and 12 are connected to the counter circuit 22A via the buffer and the inverter.

  Further, the sensor IC 95 is provided with IN2 as a control terminal constituting the time control means 23, and is connected to the counter circuit 22A. A control signal is input to the control terminal IN2 from the operation time instruction means 31 of the controller 30, and the detection operation time can be controlled. That is, as shown in the timing chart of FIG. 13, the measurement is performed when the terminal of the control terminal IN2 is HIGH, and the measurement is ended when the terminal is LOW. That is, the control terminal IN2 holds and resets the counter circuit 22A. Here, a rectangular wave is input to the control terminal IN2, the counter circuit 22A is reset at the rising edge, held at the falling edge, and integrated numerical data is serially output from the counter circuit 22A. In addition, the measurement cycle can be changed dynamically even during measurement. Thereby, the measurement accuracy and response speed can be changed dynamically.

  As described above, in this embodiment, although the accuracy of measurement subject to hardware restrictions does not change, the oscillation frequency is integrated and the distance is calculated by the average value. Therefore, the resolution is increased by increasing the integration time. Can be measured. That is, the total resolution can be improved by continuously performing the measurement with the same resolution. In addition, the integration time from the external device, that is, measurement accuracy and speed can be controlled.

  The counter circuit 22A has 32-bit outputs 0 to 31, and each is connected to a parallel output circuit 24A and a serial output circuit 24B. The parallel output circuit 24A converts the serial signal output from the counter circuit 22A into a parallel signal and outputs the parallel signal. Each output is output from 8-bit parallel output terminals POUT0 to POUT7. On the other hand, the serial output circuit 24B outputs the serial signal output from the counter circuit 22A from the serial output terminal SOUT according to the clock input from the external clock terminal CLK. As described above, the sensor IC 95 has two parallel and serial output terminals, and the counted oscillation frequency can be obtained as a digital signal value in a desired format. These output values are received by the controller 30 or the like, and a change in the distance between the sensor head 10 and the measurement object WK is calculated.

  In the above displacement sensor, the sensor itself oscillates at a high frequency due to the planar coil and the internal capacitance, and a digital output can be obtained by a counter built in the sensor. In particular, high resolution can be realized by using a high frequency band of 200 to 300 MHz. Moreover, it has the advantage that it is not influenced by the thickness of a measuring object. As described above, a change in the position of a measurement object such as a conductive substance facing the sensor head 10 can be detected with a high resolution of the order of nanomicron to submicron. In addition, the conventional displacement sensor merely rectifies the obtained voltage and current waveforms, has no idea of integration, and the oscillation frequency is fixed in hardware. In contrast, in this embodiment, the distance measurement performance can be changed by controlling the displacement sensor from the outside and changing the integration time. Specifically, the responsiveness can be improved by reducing the integration time, and the accuracy can be improved by increasing the integration time.

  Note that the conductive substance that is the measurement object is mainly a metal, but it is also possible to measure the approach distance of a conductive substance that is not a metal, such as a conductive liquid.

  The displacement sensor system and displacement sensor of the present invention are used for displacement measurement / vibration / object motion detection in a wide range of areas such as home appliances, measuring equipment, medical / welfare equipment, production line equipment, security equipment, exercise equipment, game machines, etc. it can. In particular, it can be suitably used for authenticity analysis of banknotes that require highly accurate measurement, detection of the level of a fuel cell, and the like. Also, since it is suitable for thinning and miniaturization, it can be easily installed in a narrow space. Furthermore, it is possible to detect not only the distance measurement in a non-contact manner but also the distance to the measurement object in contact with the planar distance measurement region, which can be suitably used for tablets, touch panels, fingerprint sensors, and the like.

It is a block diagram which shows the principle of operation of an eddy current type displacement sensor. It is a graph which shows a mode that the oscillation frequency of an oscillation circuit changes according to the distance of a conductor and sensor IC. It is a block diagram which shows the structure of the displacement sensor system which concerns on embodiment of this invention. It is a circuit diagram which shows the oscillation circuit of a displacement sensor. It is a block diagram which shows the structure of a displacement sensor. It is a figure which shows a square spiral coil, (a) is a top view, (b) shows sectional drawing, respectively. It is a figure which shows a round spiral coil, (a) is a top view, (b) shows sectional drawing, respectively. It is a figure which shows the square spiral coil made into 2 layer structure, (a) is a top view, (b) shows sectional drawing, respectively. It is a figure which shows the round spiral coil made into 2 layer structure, (a) is a top view, (b) shows sectional drawing, respectively. It is an external appearance perspective view of a displacement sensor system. It is an external appearance perspective view which shows another displacement sensor system. It is a block diagram of sensor IC. It is a timing chart which shows operation | movement of sensor IC of FIG.

DESCRIPTION OF SYMBOLS 100 ... Displacement sensor system 1 ... Planar coil 2, 3 ... Square spiral coil; 4, 5 ... Round spiral coil 10 ... Sensor head; 12 ... Lead; 14 ... Board | substrate 20 ... Sensor main body; 22 ... Frequency detection means; ... Counter circuit 24 ... Digital output means; 24A ... Parallel output circuit; 24B ... Serial output circuit 30 ... Controller; 31 ... Operation time instruction means 72 ... CMOS inverter (for oscillation); 73 ... CMOS inverter (for buffer)
76 ... Oscillation circuit; 77 ... Frequency counter; 78 ... Buffer circuit; 79 ... Control circuit 80 ... Stabilization circuit; 95 ... Sensor IC; 98 ... Display C1 ... Capacitor; L1 ... Oscillation coil; R1 ... Resistance component; Measurement object

Claims (6)

A displacement sensor system capable of measuring a distance between a measurement object and a contactless object,
A planar coil;
An oscillation circuit electrically connected to the planar coil;
Frequency detecting means capable of detecting a change in the oscillation frequency of the oscillation circuit according to the distance between the measurement object close to the planar coil and the planar coil;
Digital output means capable of outputting the oscillation frequency detected by the frequency detection means as a digital signal;
Time control means capable of controlling a detection operation time for detecting an oscillation frequency by the frequency detection means;
A controller having an operation time instruction means capable of sending a control signal instructing a detection operation time to the time control means;
With
A frequency type displacement sensor that calculates a change in the distance between the object to be measured and the planar coil based on the oscillation frequency detected by the frequency detection means, and that can output the calculation result as a digital value by the digital output means. A system,
The detection operation time is variable according to the measurement accuracy of the distance measurement and the response time until the distance measurement result is obtained .
The frequency detection means is composed of a frequency counter capable of counting and integrating the oscillation frequency,
The operation time instruction means is configured to control the accumulated time of the frequency counter,
The frequency counter is configured to calculate a distance measurement result after continuously performing frequency counting a plurality of times,
A displacement sensor system, wherein the frequency counter and the digital output means are configured by a packaged IC . The displacement sensor system according to claim 1,
The frequency counter is configured to control the integration time with a rectangular wave input from the operation time instruction means,
The frequency counter is reset at the rising edge of the rectangular wave, the count operation is held at the falling edge, and the count value accumulated up to that point is output as serial data by the digital output means. system. The displacement sensor system according to claim 1 or 2 ,
A displacement sensor system, wherein an oscillation frequency of the oscillation circuit is 30 MHz or more. The displacement sensor system according to any one of claims 1 to 3 ,
The displacement sensor system, wherein the planar coil is a round or square spiral coil. In the displacement sensor system according to any one of claims 1 to 4 ,
The oscillation circuit, the frequency detection means and the digital output means are mounted on the same substrate to constitute a sensor body,
2. The distance measuring sensor system according to claim 1, wherein the planar coil constitutes a sensor head protruding from the sensor body. In a displacement sensor that can measure the distance to the measurement object without contact,
A planar coil;
An oscillation circuit electrically connected to the planar coil;
The change in the oscillation frequency of the oscillation circuit is detected by counting and integrating the oscillation frequency of 30 MHz or more according to the distance between the measurement object close to the planar coil and the planar coil, and the integrated value A frequency counter that can output digital values,
Digital output means capable of outputting the oscillation frequency detected by the frequency counter as a digital signal;
Time control means capable of controlling the integration time for detecting the oscillation frequency with the frequency counter;
With
Based on the oscillation frequency detected by the frequency counter, the distance change between the measurement object and the planar coil is calculated, and the calculation result can be output as a digital value by the digital output means ,
The frequency counter is configured to calculate a distance measurement result after continuously performing frequency counting a plurality of times,
A displacement sensor, wherein the frequency counter and the digital output means are constituted by a packaged IC .

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