JP2005210146A - Minute difference detecting circuit between two circuit elements, position detecting device employing same, and discrimination detecting device for detecting fault or presence/absence of magnetic body or conductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a minute difference detecting circuit between two circuit elements capable of detecting the minute inductance difference between two coils or the minute capacity difference between two capacitors, and propose a position detecting device and a discrimination detecting device of the fault or the presence/absence of a conductor. <P>SOLUTION: Power is applied like a step to an RLC circuit comprising the two coils or two capacitors, the detection potential difference corresponding to the difference between the two circuit elements is integrated, a driving voltage to the RLC circuit is switched every time the driving voltage exceeds a predetermined voltage, a pulse sequence inversely proportional to the difference between circuit elements is generated, and the difference between the two circuit elements is identified by knowing a frequency. Since the smaller the difference between the two circuit elements is, the more an discrimination resolution can be improved; the device is applicable to a proximity sensor, a magnetic flaw detection device, and a metallic foreign matter inspection device etc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a comparison detection circuit such as a coil and a capacitor, and in particular, a circuit for identifying and detecting a minute inductance difference of a coil or a minute capacitance difference of a capacitor with sufficient resolution, and a detection circuit for a minute inductance difference of a coil. It relates to the position detection device which has.

  Precise measurement of a coil, a capacitor, etc. is performed by comparison with a resistance, coil, capacitor, etc. as a reference using an impedance bridge (for example, Japanese Patent Laid-Open No. 5-296866). However, in these measuring means, the difference between the value of the reference element and the element to be inspected and the output voltage are linearly proportional, so when the difference between the two is small, the output is also small and it may be difficult to identify. It was. Further, these are level difference tests using analog signals, and high-precision AD converters are required for digitization, and cost reduction is difficult.

  In actual application, there are many demands for detecting minute changes in the constants of these coils and capacitors. For example, in an eddy current type proximity sensor, detection of minute changes in inductance is important in order to detect the approach of an object from as far as possible. Further, in an example in which the control system detects and balances changes to be controlled by two coils or two capacitors, it is important to know a minute change from the equilibrium position with sufficient resolution. Furthermore, detection of flaws in metal objects or detection of metallic foreign objects in foods and clothing, etc. all detect changes in the small inductance of the coil, and in these devices, the two detection coils are referred to each other. When differentially used as a coil, it is important to detect a small inductance difference between the two coils with high resolution.

Japanese Patent Application Laid-Open No. 5-296866 “Pressure Sensor”

  Accordingly, an object of the present invention is to propose a minute difference detection circuit of two circuit elements that can detect a minute inductance difference between two coils or a minute capacitance difference between two capacitors at a low cost. It is possible to realize a defect or presence / absence identification inspection apparatus.

  The basic concept of the small difference detection circuit of two circuit elements according to the present invention is that a constant difference between two coils or two capacitors to be compared corresponding to stepped energization including two coils or two capacitors to be compared. An RLC circuit that outputs a detection potential difference corresponding to the voltage, a voltage comparator that exhibits a hysteresis characteristic with high and low level thresholds by inputting a signal proportional to the detection potential difference, and first and second different drives The voltage comparator, which is composed of an energization control unit that drives the RLC circuit with voltage and an identification control unit, has a hysteresis characteristic, and the signal proportional to the detected potential difference reaches the high level and low level thresholds. Then, the output level is switched, and the energization control unit reduces the voltage comparator input after the voltage comparator input reaches the high level threshold, and the voltage after the voltage comparator input reaches the low level threshold. The driving voltage applied to the RLC circuit is switched so that the comparator input increases, and if the driving voltage does not change within a predetermined time, the driving voltage is forcibly switched, and the oscillation time is set with the predetermined time as the maximum half cycle. The self-excited oscillation circuit is configured to be inversely proportional to the constant difference between the two comparison target coils or the two capacitors, and the identification control unit calculates the constant difference between the two comparison target coils or the two capacitors from the period of the pulse train. It is characterized by identifying.

  The present invention as defined in claim 2 integrates the detection potential difference of claim 1, obtains a voltage proportional to the constant difference between the two circuit elements, and inputs the voltage to a voltage comparator having hysteresis characteristics, so that the circuit constant can be easily set. And it has a strong characteristic against noise.

  The present invention as defined in claim 3 is a configuration further comprising an integration circuit between the integration circuit of claim 2 and the voltage comparator, and generates a pulse train having a period corresponding to the difference between two coils or two capacitors, By counting minute intervals, the period is known and digital data of constant difference between two coils or two capacitors is obtained.

  The difference between the output of the first integration circuit and the reference potential is used as an input to the second integration circuit. The reference potential is the average voltage output of the first integration circuit or the output of the first integration circuit immediately before switching the energization drive voltage. The reference potential is set, and the output of the first integration circuit is forcibly reset to a predetermined potential each time the energization drive voltage is switched, and the potential is set as the reference potential.

  The present invention as defined in claims 1, 2 and 3 is characterized in that the identification period can be improved because the pulse period becomes longer as the constant difference between the two coils or the two capacitors becomes smaller.

  A fourth aspect of the present invention provides a means for identifying a pulse period in the present invention as defined in the first, second, and third aspects, wherein two coils or two to be compared are compared by a minute interval pulse count directly or after counting down a pulse train. It is characterized by identifying a constant difference between two capacitors.

  A fifth aspect of the present invention provides a method for determining the magnitude relationship between two circuit elements in the present invention as defined in the first, second and third aspects. That is, since the identified pulse period only indicates the absolute value of the constant difference between the two coils or two capacitors to be compared, the two circuit elements are determined from the direction of change in the voltage comparator output and the direction of energization to the RLC circuit. Identify the magnitude relationship.

  Claims 6 and 7 show examples of the RLC circuit when two coils are used in the present invention of claims 1, 2 and 3. That is, claim 6 shows a bridge circuit including two coils and a resistor, and claim 7 is based on a series circuit of two coils, and a resistor is further inserted in series or connected in parallel with the coil. 3 shows a circuit in which the potential difference between the midpoint equivalent portion potential and the time-average potential of the midpoint equivalent portion potential is a detected potential difference.

  Claims 8 and 9 show examples of RLC circuits that can be used when two capacitors are used in the present invention of Claims 1, 2 and 3. That is, claim 8 shows a bridge circuit including two capacitors and a resistor, and claim 9 is a series circuit of two capacitors and a resistor, and the time corresponding to the midpoint equivalent potential and the midpoint equivalent potential between the two capacitors. A circuit in which a potential difference from an average potential is a detection potential difference is shown.

  According to a tenth aspect of the present invention, there is provided a minute difference detection circuit comprising two coils whose constants are changed at least according to the position of a movable body made of a magnetic body or a conductor, and two circuit elements to be compared with the two coils. The position detecting device is configured to detect the position of the movable body by identifying a constant difference between the two coils.

  According to the eleventh aspect of the present invention, in the position detection device according to the tenth aspect, the equilibrium position of the RLC circuit including two coils is shifted, the detection sensitivity with respect to the direction of increase / decrease of the inductance that changes due to the proximity of the magnetic body and the conductor is changed, A high-sensitivity position detection device is realized by compensating for sensitivity in the case of proximity to a small conductor.

  The present invention of claim 12 shows an inspection apparatus characterized by having two coils and identifying and detecting a defect or the presence or absence of a magnetic substance or a conductor from an inductance difference between the two coils with reference to the other coil. Yes.

  The small constant difference detection circuit for two circuit elements according to the present invention described above energizes the RLC circuit including two coils or two capacitors in a stepped manner, and the inductance difference between the two coils or the two capacitance differences. A pulse difference having a period inversely proportional to the constant difference between the two circuit elements is generated by comparing a potential difference corresponding to, or an integrated value thereof with a predetermined voltage, and the period is identified by a minute interval pulse count. Therefore, the smaller the difference between these constants, the longer the pulse train period and the easier the identification. If the position detection device is constituted by two coils whose inductance of at least one coil varies depending on the position of the movable body and a small constant difference detection circuit of two circuit elements, the position of the movable body can be detected from a distance.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention, a minute difference detection circuit for two circuit elements, and an apparatus using the same will be described below with reference to the drawings.

  FIG. 1 shows a first embodiment of the present invention, and shows a circuit for identifying and detecting an inductance difference between two coils as a specific example of a minute difference detection circuit for two circuit elements. In the figure, a coil 11 and a resistor 13 are connected in series, and a coil 12 and a resistor 14 are connected in series to constitute an RLC circuit. The resistors 13 and 14 have the same value, and the inductance difference between the coils 11 and 12 appears as a detected potential difference between the connection point between the resistor 13 and the coil 11 and between the connection point between the resistor 14 and the coil 12. The first integration circuit 15 integrates the detected potential difference and outputs it to the first integration capacitor 16. The first integration circuit 15 includes a voltage-current conversion circuit and a first integration capacitor 16. The voltage comparator 17 having hysteresis characteristics inputs the first integrated voltage appearing on the first integrating capacitor 16, compares it with a predetermined voltage, changes its output, and inputs it to the flip-flop 18. The flip-flop 18 inverts its output at the edge where the output of the voltage comparator 17 changes, and an RLC circuit composed of the coils 11 and 12 and the resistors 13 and 14 is connected to its complementary outputs 1c and 1d. ing.

  The operation of the first embodiment shown in FIG. 1 will be further described with reference to FIG. 2A shows the waveform of the output 1d of the flip-flop 18, and FIG. 2B shows the waveform of the first integration voltage appearing in the first integration capacitor 16. FIG.

  In FIG. 1, when the RLC circuit is energized stepwise, current does not immediately flow through the series circuit of the coil 11 and the resistor 13 and the series circuit of the coil 12 and the resistor 14 due to the inductance of the coils 11 and 12, but the current gradually increases. It is a well-known fact that the transient phenomenon reaches a certain value. Assuming that the currents flowing through the resistors 13 and 14 are I1 and I2, respectively, the detected potential difference ΔV between the coils 11 and 12 is the difference in voltage drop between the coils 11 and 12, so that the respective inductances are represented by L1 and L2. ΔV is represented by L1 * I1′−L2 * I2 ′. Here, I1 'indicates that the current I1 is time-differentiated.

The resistors 13 and 14 are represented by R as the same, and when the applied voltage is E, I1 = (E / R) (1-exp (−Rt / L1)), I2 = (E / R) (1-exp (−Rt / L2)). E represents an applied voltage, t represents time, and exp represents an exponential function.
The integrated value of the detected potential difference ΔV appears on the first integrating capacitor 16 as the first integrated voltage by the first integrating circuit 15. If the conversion gain by the voltage-current conversion circuit is G, the current flowing into the first integrating capacitor 16 is GΔV, that is, G (L1 * I1′−L2 * I2 ′), but the current flowing into the first integrating capacitor 16 Is substantially integrated to become charge Q, and charge Q is Q = G (L1 * I1-L2 * I2) = G (E / R) (L1-L2-L1 * exp (-Rt / L1) + L2 * exp (-Rt / L2)). This asymptotically approaches G (E / R) (L1-L2) with time. Therefore, if the capacitance of the first integrating capacitor 16 is C, the first integrated voltage appearing at the terminal is a voltage G (E / R) (L1-L2) / C proportional to the inductance difference between the coils 11 and 12. It will be asymptotic.

  When the inductance of the coil 11 is smaller than the inductance of the coil 12, when the output 1d to the output 1c are energized through the RLC circuit, the voltage of the first integrating capacitor 16 increases as indicated by reference numeral 21, and the first predetermined voltage 23, the voltage comparator 17 changes the output level as indicated by reference numeral 27 in FIG. 2C, and the flip-flop 18 inverts the outputs 1c and 1d at the edge where the output 27 changes, and supplies power to the RLC circuit. Is reversed from the output 1c to the output 1d. Since the polarity of the detected potential difference between the coils 11 and 12 changes, the first integrating circuit 15 discharges the electric charge of the first integrating capacitor 16, and the first integrated voltage changes as indicated by numeral 22. When the voltage 22 reaches the second predetermined voltage 24, the voltage comparator 17 changes the output level as indicated by numeral 27 in FIG. 2C, and the flip-flop 18 outputs its output 1c, 1d at the edge where the output 27 changes. Is reversed, the energization direction of the RLC circuit is reversed from the output 1d to the output 1c, and this is repeated.

  The voltage comparator 17 having hysteresis characteristics has a hysteresis with a potential that is a certain amount higher than a reference potential created therein as a first predetermined voltage and a potential that is a certain amount lower than the reference potential as a second predetermined voltage. As described above, the voltage of the first integrating capacitor 16 is controlled to decrease when reaching the first predetermined voltage 23, and to increase when reaching the second predetermined voltage 24. And a predetermined voltage 23, 24.

  FIG. 3 shows the first and second predetermined voltages 23 and 24 of the voltage 21, 22 and voltage comparator 17 appearing on the first integrating capacitor 16 in an enlarged manner. A dotted line 31 shows a voltage waveform of the first integrating capacitor 16 when the inductance difference between the coils 11 and 12 becomes larger. When the inductance difference between the coils 11 and 12 becomes larger, the rise and fall become steep. This shows that the period of change is shortened. As can be seen from the figure, when the inductance difference between the coils 11 and 12 is increased, the period of the pulse train of the outputs 1c and 1d of the flip-flop 18 is naturally shortened. Since the voltage of the first integrating capacitor 16 and the fluctuation period of the outputs 1c and 1d of the flip-flop 18 are inversely proportional to the inductance difference ΔL of the coils 11 and 12, they change as shown by the curve 41 in FIG.

  The output 1d of the flip-flop 18 is input to the counter 19 and counted down as indicated by the number 2a in FIG. 2 (e) and the number 2b in FIG. 2 (f), and then input to the microcomputer 1a (indicated by the number 1e). The period of the output 1d is measured by counting the minute interval pulse 2c using a built-in counter, and the inductance difference between the coils 11 and 12 is identified.

  When the inductance difference between the coils 11 and 12 is smaller than expected, for example, as shown in FIG. 2B, the first integrated voltage indicated by number 25 reaches the first predetermined voltage indicated by number 26. If not, the voltage comparator 17 does not invert the output 1b, and therefore the output of the flip-flop 18 does not change. If the first integrated voltage indicated by reference numeral 25 does not reach the first predetermined voltage (in this case indicated as 26) within a predetermined time, the microcomputer 1a outputs a pulse 28 (output 1f in FIG. 1) and its edge To change the state of the flip-flop 18. Reference numeral 29 in FIG. 2A indicates that the state of the output 1 d of the flip-flop 18 has been changed by the pulse 28.

  The digital value obtained by counting the pulse period of the output 1d of the flip-flop 18 by counting the minute interval pulse 2c corresponds to the inductance difference between the coils 11 and 12, but this is an absolute value, and the inductance of any of the coils is large. I don't know if it exists. The magnitude relationship between the coils 11 and 12 is determined by the direction in which the voltage comparator 17 output 1b changes and the energization direction to the RLC circuit, that is, the level of the output 1d. When the voltage of the first integrating capacitor 16 reaches the first predetermined voltage 23, the voltage comparator 17 turns the output to a low level, and when the voltage reaches the second predetermined voltage 24, the output turns to a high level. The output 1b can be determined by the level of the output 1d when the output 1b changes from low level to high level and from high level to low level. That is, in the left half of FIG. 2, the output 1d is high at the rising edge of the output 27 (1b) shown in FIG. 2C, so the inductance of the coil 12 is large, and in the right half, the rising edge of the output 27 (1b). Since the output 1d is at a low level, it can be determined that the inductance of the coil 11 is large.

  FIG. 4 shows the relationship 41 between the pulse period T of the output 1d and the inductance difference ΔL between the coils 11 and 12, but the measurable pulse period T is a predetermined time set as the microcomputer 1a outputs the pulse 28. The upper limit is set by and the lower limit is set by the time interval of the minute interval pulse 2c. That region is illustrated by the number 42.

  In FIG. 1, the energization control unit is mainly composed of a flip-flop 18, and the identification control unit is composed of a counter 19 and a microcomputer 1a. This is merely an example, and the function of the counter 19 can be incorporated in the microcomputer 1a even if an output amplifier circuit capable of high voltage driving is provided following the flip-flop 18. Furthermore, the processing expected from the microcomputer 1a can be configured only by a logic circuit.

  In the circuit shown in FIG. 1, the energization control unit drives the RLC circuit by inverting the output of the flip-flop 18 at the output change edge of the voltage comparator 17. This is a circuit that assumes a general case where the magnitude relationship between the coils 11 and 12 is not determined, and the input of the voltage comparator 17 is decreased after the input of the voltage comparator 17 reaches the first predetermined voltage that is a high level threshold. In the direction, after the input of the voltage comparator 17 reaches the second predetermined voltage which is a low level threshold value, the RLC circuit is energized and driven in the direction of increasing the input of the voltage comparator 17. It is also possible to drive the RLC circuit by removing the flip-flop 18 and amplifying the output of the voltage comparator 17 if the magnitudes of the coils 11 and 12 to be compared are determined within the range of use. The bridge circuit including the resistors 11 and 12 in addition to the coils 11 and 12 is intentionally lost in balance, and the integrated voltage of the detected potential difference is a condition in which the increasing / decreasing direction is always constant at the rising and falling edges of the driving voltage. It is the same.

  The above-described embodiment is a self-excited oscillation circuit that outputs a trigger from the microcomputer 1a every predetermined time. The oscillation period is maximized and modulated such that the oscillation period changes in inverse proportion to the inductance difference between the two coils 11 and 12. It is an example. Although the above configuration is used to minimize the analog circuit, a configuration having an oscillation circuit may be used.

  FIG. 5 shows a second embodiment of the present invention, and shows a circuit for detecting and identifying the capacitance difference between two capacitors as a specific example of the minute difference detection circuit for two circuit elements. In the figure, two capacitors 51 and 52 are respectively connected in series with resistors 13 and 14 having the same constant, and the respective circuits are connected in parallel to constitute an RLC circuit. The first integrating circuit 15 receives the potentials of the connection points of the resistor 13 and the capacitor 51 and the connection points of the resistor 14 and the capacitor 52 of the RLC circuit as inputs and integrates the detected potential difference between these connection points to represent the first integration capacitor 16. . The other circuit configuration is the same as that shown in FIG.

  When stepped energization is performed on the capacitors 51 and 52 in FIG. 5 through the resistors 11 and 13, respectively, excessive voltages appear in the capacitors 51 and 52, and asymptotically become equal to the applied voltage, respectively. When the detected potential difference, which is a difference, is integrated, the integrated value gradually approaches a value proportional to ER (C1-C2). Here, E is the applied voltage, R is the resistance value of the resistors 13 and 14, and C1 and C2 are the capacitances of the capacitors 51 and 52, respectively. A pulse train having a period inversely proportional to the capacitance difference between the capacitors 51 and 52 is obtained at the outputs 1c and 1d of the flip-flop 18, and the capacitance difference is identified by the counter in the microcomputer 1a with a minute interval pulse count. However, the operation principle is the same as that in the case of the inductance difference shown in the first embodiment shown in FIG.

  FIG. 6 shows a third embodiment of the present invention, and shows a circuit for discriminating and detecting an inductance difference between two coils as a specific example of a minute difference detection circuit of two circuit elements. Although the purpose and function are the same as those of the first embodiment of FIG. 1, the RLC circuit and the means for energizing the RLC circuit are different. That is, in FIG. 6, the coils 61 and 62 are connected in series, and the resistors 13 and 14 are inserted and connected in series to form a vertically symmetrical structure. The reference potential is configured by a reference potential generation circuit 63 with the connection point between the coils 61 and 62 as a midpoint, and the first integration circuit 15 integrates the difference between the midpoint potential and the output of the reference potential generation circuit 63. ing. In the figure, a reference potential generation circuit 63 forms a low-pass filter with a resistor and a capacitor, and the time average of the midpoint potential is used as the reference potential.

  The energization of the RLC circuit is not driven by the complementary output of the flip-flop 18, but the RLC circuit is driven from the output 1 d of the flip-flop 18 via the energization control circuit 64. The energization control circuit 64 has first and second drive voltages to drive the RLC circuit. The first and second drive voltages are two types of positive voltages, even if they are positive and negative voltages, respectively. One of them may be ground potential. The detection potential difference corresponding to the energizing voltage that rises stepwise and the detection potential difference corresponding to the energizing voltage that falls stepwise are theoretically reversed in polarity, and when they are integrated as they are, one is integral addition and the other is integral subtraction It is used to become. The waveform appearing at the output of the integrating circuit 15 is the same as that shown in FIG.

  Accordingly, the third embodiment shown in FIG. 6 is different from the first embodiment shown in FIG. 1 in the RLC circuit, and the energization driving method is different, but the operation principle is the same, so detailed description thereof is omitted. . Since the current values flowing through the coils 61 and 62 in series are the same, the DC resistance of the coils 61 and 62 is almost completely canceled as compared with the first embodiment. In consideration of the fact that these DC resistances are likely to change with temperature, this is an embodiment in which the influence of temperature can be further eliminated.

  FIG. 7 shows a fourth embodiment of the present invention, and shows a circuit for discriminating and detecting a capacitance difference between two capacitors as a specific example of a minute difference detection circuit of two circuit elements. Although the purpose and function are the same as the second embodiment of FIG. 5, only the RLC circuit is different. That is, in FIG. 7, capacitors 71 and 72 are connected in series, and resistors 13 and 14 are inserted and connected in series to constitute a vertical object. The reference potential is constituted by a reference potential generation circuit 63 with the connection point between the capacitors 71 and 72 as a midpoint, and the first integration circuit 15 integrates the difference between the midpoint potential and the output of the reference potential generation circuit 63. ing. In the figure, the reference potential generating circuit 63 employs a simple circuit in which a low-pass filter is constituted by a resistor and a capacitor.

  Since the fourth embodiment shown in FIG. 7 is the same as the second embodiment shown in FIG. 5 except for the RLC circuit, description of the operating principle and the like is omitted.

  FIG. 8 shows a fifth embodiment of the present invention, and shows a circuit for discriminating and detecting an inductance difference between two coils as a specific example of a minute difference detection circuit of two circuit elements. The purpose and function are the same as those of the first embodiment of FIG. 1 except that a second integration circuit 82 is inserted between the first integration circuit 15 and the voltage comparator 17. That is, in the figure, the difference between the output of the first integrating circuit 15 and the reference potential is integrated by the second integrating circuit 82 and stored in the second integrating capacitor 83, and the voltage comparator 17 stores the voltage of the second integrating capacitor 83. Is compared with a predetermined voltage to change its output 1b. In FIG. 8, the reference potential is generated by the reference potential generation circuit 81 as the time average of the output of the first integration circuit 15. The reference potential generation circuit 81 in the embodiment of FIG. 8 is configured as a simple low-pass filter using a resistor and a capacitor.

  As described in the first embodiment, a voltage proportional to the inductance difference between the two coils 11 and 12 appears in the first integrating capacitor 16. The second predetermined voltage setting is limited.

  In the fifth embodiment, the first and second predetermined voltages of the voltage comparator 17 can be set relatively easily even when a small inductance difference is detected. Since the difference between the output of the first integrating circuit 15 and its time average value is input to the second integrating circuit 82, the second integrating capacitor 83 has a voltage G (E / R) (proportional to the inductance difference between the coils 11 and 12). A voltage asymptotically appears as the product of (L1-L2) / C and time, and this voltage increases with time, so that the first and second predetermined voltage settings of the voltage comparator 17 are facilitated. This is a suitable example.

  In the example of FIG. 8, the reference potential generation circuit 81 generates the reference potential by averaging the outputs of the first integration circuit 15 over time, but the first integration circuit every time the flip-flop 18 inverts the outputs 1c and 1d. It can be realized as a circuit configuration that holds 15 outputs and uses the potential as a reference potential, or as a circuit configuration that resets to a fixed reference potential every time the flip-flop 18 inverts its outputs 1c and 1d.

  FIG. 9 shows a sixth embodiment of the present invention, and shows a circuit for discriminating and detecting a minute capacitance difference between two capacitors as a specific example of a minute difference detecting circuit of two circuit elements. The second embodiment of FIG. 5 has the same purpose and function, but differs in that a second integration circuit 82 is inserted between the first integration circuit 15 and the voltage comparator 17. That is, in FIG. 9, the difference between the output of the first integrating circuit 15 and the reference potential is integrated by the second integrating circuit 82 and stored in the second integrating capacitor 83, and the voltage comparator 17 is stored in the second integrating capacitor 83. The voltage is compared with a predetermined voltage to change its output 1b. In FIG. 9, the reference potential is generated by the reference potential generation circuit 81 as a low frequency component of the output of the first integration circuit 15.

  The relationship between the second embodiment of FIG. 5 and the sixth embodiment of FIG. 9 is the same as the relationship between the first embodiment shown in FIG. 1 and the fifth embodiment of FIG. Since the principle is the same, the detailed explanation is omitted.

  FIG. 10 shows a seventh embodiment of the present invention, and shows a circuit for discriminating and detecting an inductance difference between two coils as a specific example of a minute difference detection circuit of two circuit elements. The configuration is similar to that of the third embodiment of FIG. 6 except that a difference circuit 101 and an addition voltage circuit 102 are arranged instead of the first integration circuit 15. That is, in the same figure, the potential difference corresponding to the inductance difference between the coils 61 and 62 is the same, but the voltage generated by the addition voltage circuit 102 is added and amplified by the difference circuit 101 for voltage comparison. Input to the device 17. Other configurations are the same as those in FIGS.

  FIG. 11 shows a pulse driving voltage and a transient response waveform for explaining the operation. FIG. 11A shows the transient response when a pulse voltage is applied to the series circuit composed of the coils 61 and 62 and the resistors 13 and 14, and the pulse voltage 111, the coil 61 and the coil 62 applied to the series circuit are shown in FIG. A voltage waveform 112 appearing at the connection point is shown. A voltage waveform 112 is a detected potential difference corresponding to the inductance difference between the coils 61 and 62 and is a positive or negative voltage. However, for the sake of easy handling, the voltage generated by the addition voltage circuit 102 is added to obtain a unipolar transient response difference. The voltage 113 is input to the voltage comparator 17. When the transient response differential voltage 113 reaches the first and second predetermined voltages 23 and 24 which are the threshold values of the voltage comparator 17, the output of the voltage comparator 17 is changed, and the coils 61 and 62 and the resistors 13 and 14 are configured. The self-excited oscillation circuit is configured by inverting the voltage applied to the series circuit. FIG. 11B shows the relationship between the transient response differential voltage 113 and the first and second predetermined voltages 23 and 24.

  The operation of the other parts is the same as in FIG. However, in the example of FIG. 10, the voltage generated by the addition voltage circuit 102 needs to be set between the first and second predetermined voltages 23 and 24.

  FIG. 12 shows a position detection apparatus according to an eighth embodiment of the present invention. The detection coil 121 and the reference coil 122 wound around the magnetic core 124 indicated by the hatched portion in the detection unit 123 are configured with the same specifications, and a movable body made of a conductor or a magnetic material is moved from the left to the detection coil 121. The position of the movable body is known by detecting that the inductance of the detection coil 121 has changed in the vicinity. A resistor 13 is connected in series to the detection coil 121, a resistor 14 is connected in series to the reference coil 122, and the minute inductance difference detection circuit has the same configuration as that of the fifth embodiment shown in FIG.

  The detection coil 121 and the reference coil 122 are configured to have substantially the same inductance. However, when a conductor such as aluminum or copper or a magnetic material such as iron or ferrite comes close to the detection coil 121, the inductance changes. It is detected that there is a difference from the inductance of the reference coil 122 in accordance with the operation principle of the inductance difference detection circuit described with reference to FIGS.

  In a proximity sensor, which is one application of a position detection device, it is desirable to detect a nearby object from as far as possible. Conventionally, however, the limit is limited by fluctuations in the constant of the detection coil 121 due to temperature changes, fluctuations in circuit constants, or the like. I was receiving. In the configuration shown in FIG. 12, the detection coil 121 and the reference coil 122 are configured with the same specifications, placed in the same temperature environment, and the presence or absence of the difference is identified and detected, so that it is not easily affected by temperature fluctuations.

  When the conductor is close to the detection coil 121, the inductance is reduced due to the eddy current effect, and conversely, when the magnetic body is close, the inductance is increased. Since the direction of increase / decrease in the inductance is reversed, the identification result is changed in the direction in which the increase / decrease of the inductance of the reference coil 122 is changed, and the proximity of the movable body and the magnetic body is detected by changing the digital threshold and determining the proximity of the movable body. Can also be used.

  Also, in the case of a proximity sensor for the purpose of detecting the proximity of a metal or a magnetic material as a reference coil with one of the two coils as a constant, the balance of the RLC circuit including the two coils and the resistance is intentionally broken, and the other coil It is set so that the inductance difference between the two increases as the inductance increases, and the inductance difference decreases as the inductance decreases. When the conductor is close, the inductance decreases, and when the magnetic body is close, the inductance increases. However, since the change in the former is generally small, the detection sensitivity can be compensated by setting as described above, and high sensitivity detection is possible.

  In addition to changing the digital threshold, there is also means for adaptively changing the conversion gain of the first integration circuit 15 or the second integration circuit 82. That is, whether the inductance of the detection coil 121 is larger or smaller than that of the reference coil 122 can be determined from the level of the output 1d at the rising edge or the falling edge of the voltage comparator 17, so that the inductance of the detection coil 121 is A configuration may be adopted in which the gain of the first integration circuit 15 or the second integration circuit 82 is changed to a small value while it is identified as large.

  FIG. 13 shows a schematic configuration of a magnetic flaw detection apparatus as a specific example of a conductor defect identification inspection apparatus according to the ninth embodiment of the present invention. FIG. 13A shows the outline of the detection unit, and FIG. 13B shows the output dipulse waveform. In the figure, the magnetic flaw detector is composed of two detection coils 131 and 132, a detection circuit 130, scanning mechanism means (not shown), and the like. The two detection coils 131 and 132 are metal to be inspected. The subject 133 is disposed in the vicinity of the subject 133, and the subject 133 is moved along the arrow 134 by the scanning mechanism means. Since the detection circuit 130 is the same as that shown in FIG. 8, the description of the specific contents and operation principle of the detection circuit 130 will be omitted.

  The detection circuit 130 intermittently energizes the detection coils 131 and 132 to generate a pulsed magnetic flux 135. The pulsed magnetic flux 135 tends to penetrate from the surface of the subject 133 that is a metal, but an eddy current flows on the surface of the subject 133 in a direction that prevents the change of the magnetic flux, and the inductance of the detection coils 131 and 132 is increased. Apparently decrease. Here, if there is a flaw on the surface of the subject 133, the eddy current does not flow easily, the decreasing tendency of the inductance of the detection coils 131 and 132 is weakened, and the apparent inductance increases. If the scratch on the surface of the subject 133 is in the magnetic field distribution of the detection coil 131, the inductance of the detection coil 131 becomes larger than usual.

  Since the magnetic flaw detector is a device for confirming the presence or absence of scratches or defects that should not be present, the density of the scratches or defects is naturally low. Even if there is a scratch directly under the detection coil 131, the detection coil 132 The probability that a flaw is also present on the surface of the subject 133 directly below should be very small. The reverse is also true. Since the detection circuit 130 shown in FIG. 13A is based on the detection circuit of the inductance difference between the detection coils 131 and 132, it is possible to inspect the subject 133 for scratches and defects using the other detection coil side as a reference. become. It should be noted that the scanning mechanism means moves relatively while maintaining the relationship between the detection coils 131 and 132 and the subject 133 under the same conditions as much as possible.

  In the present embodiment, the arrangement of the detection coils 131 and 132 is along the moving direction 134 of the subject 133. Therefore, if the surface of the subject 133 is scratched and detected as an inductance change of the detection coil 131, the detection coil 132 is also moved after the time determined by the movement time of the subject 133 and the distance between the detection coils 131 and 132. It should appear as a change in inductance. FIG. 13B shows how the inductance difference detected by the detection circuit 130 changes. The horizontal axis 136 represents time, and the vertical axis 137 represents the inductance difference. Reference numeral 138 indicates the output level when the surface of the subject 133 is not damaged and the inductances of the detection coils 131 and 132 are balanced. Reference numerals 139 and 13a respectively indicate that a flaw on the surface of the subject 133 changed the inductance of the detection coil 131 and then changed the inductance of the detection coil 132. Although depending on the size of the flaw, the size of the detection coils 131 and 132, and the relative positional relationship, the change in the inductance difference appears as a dipulse waveform in which two positive and negative pulses are continuous as shown in FIG.

  In the above-described magnetic flaw detector, the arrangement conditions of the two detection coils 131 and 132 and the subject 133 should be the same, but the magnetic flaw detector is assumed on the assumption that a dipulse waveform appears as shown above. If configured, the arrangement conditions of the two detection coils 131 and 132 and the subject 133 can be relaxed, and the accuracy of detection confirmation for interference signals such as noise can be improved.

  The above-described embodiment is a magnetic flaw detector for detecting the presence or absence of a flaw or a defect in a metal or a magnetic material.

  The principle operation and the like of the present invention have been described above using the embodiments. In these embodiments, the RLC circuit is often energized by reversing the energization direction. If one end of the RLC circuit is considered as a reference potential, the first drive voltage and the second drive voltage are set to a voltage that is larger or smaller than the reference potential by the same voltage. In the embodiment of FIG. 6, the energization control means has the first and second drive voltages to drive the RLC circuit, but naturally one drive voltage may be zero. The means for alternately inverting the energization direction is one example of the energization control means, but it is frequently used because the drive circuit and the drive waveform are easily symmetric.

  Furthermore, not only elements, materials, etc. other than those described in the embodiments are used, but also a detection circuit for a minute inductance difference and a minute capacitance difference is embodied based on the spirit of the present invention in configurations other than those described in the embodiments. Is possible. In particular, in the above description, the integration circuit is composed of a voltage-current conversion circuit and a potential difference integration capacitor. However, this is for convenience in circuit configuration, and there is no problem as an integration circuit with other configurations. In addition, although the position detection device and the conductor defect identification / inspection inspection device have been described using inductance detection, the invention can be applied to other application devices. As described above, it is a matter of course that materials, circuit elements, configurations, and the like can be changed without departing from the spirit of the present invention, and the above description does not limit the scope of the present invention.

  The present invention is a simple detection circuit that generates a pulse train having a period inversely proportional to the small constant difference between the two circuit elements, and is able to expand and identify the small circuit constant difference. It is suitable for applications such as proximity sensors, magnetic flaw detectors, metal foreign object inspection devices, proximity sensors that require minute capacitance difference detection, shaft displacement detection devices, etc. that realize a circuit and require minute inductance difference detection.

The inductance difference detection circuit of two coils which is a 1st Example is shown. The signal waveform of each point of the embodiment of FIG. 1 is shown. The relationship between the pulse width and a predetermined level is shown. The relationship between a pulse period and an inductance difference is shown. 2 shows a capacitance difference detection circuit of two capacitors according to a second embodiment. The inductance difference detection circuit of two coils which is a 3rd Example is shown. 4 shows a capacitance difference detection circuit for two capacitors according to a fourth embodiment. 10 shows a minute inductance difference detection circuit according to a fifth embodiment. 9 shows a minute capacitance difference detection circuit according to a sixth embodiment. The inductance difference detection circuit of two coils which is a 7th Example is shown. FIG. 11 shows signal waveforms at respective points in the embodiment of FIG. The position detection apparatus which is an 8th Example is shown. 9 shows a schematic configuration of a magnetic flaw detector according to a ninth embodiment.

Explanation of symbols

11, 12 ... coil, 13, 14 ... resistance,
15 ... 1st integration circuit, 16 ... 1st integration capacitor,
17 ... voltage comparator, 18 ... flip-flop,
19 ... counter, 1a ... microcomputer,
1b ... voltage comparator output, 1c, 1d, 1f ... output,
1e Counter output,
21, 22... First integrator circuit output voltage, 23... First predetermined voltage,
24 ... second predetermined voltage, 25 ... first integration circuit output voltage,
26: first predetermined voltage, 27: voltage comparator output,
28 ... Reset pulse, 29 ... Waveform of flip-flop output 1d,
2a, 2b, counter output waveform, 2c, minute interval pulse,
31 ... first integrator circuit output voltage,
41 ... Relationship between inductance difference and pulse period,
42 ... measurable area,
51, 52 .. capacitor
61, 62 .. coil, 63... Reference potential generation circuit,
64 ... energization control circuit,
71, 72 .. Capacitor, 81... Reference potential generation circuit,
82 ... second integration circuit, 83 ... second integration capacitor,
101 ... Difference circuit, 102 ... Addition voltage circuit,
111 ... pulse voltage, 112 ... detection potential difference,
113 ... Transient response differential voltage,
121 ... detection coil, 122 ... reference coil,
123... Detection unit, 124 ... magnetic core,
130... Detection circuit, 131, 132 .. detection coil,
133 ... subject, 134 ... moving direction,
135 ... magnetic flux, 136 ... time,
137 ... inductance difference,
138, 139, 13a .. Inductance difference waveform,

Claims (12)

An RLC circuit that includes two coils or two capacitors to be compared and outputs a detection potential difference corresponding to a constant difference between the two coils or two capacitors to be compared in response to stepwise energization, and a proportional relationship with the detection potential difference A voltage comparator having a high level and a low level threshold as input and having hysteresis characteristics, an energization control unit for driving the RLC circuit with first and second different drive voltages, and identification control The voltage comparator with hysteresis characteristics switches the output level when the signal proportional to the detected potential difference reaches the high level and low level thresholds, and the energization control unit has a high voltage comparator input level. The voltage applied to the RLC circuit is switched off so that the voltage comparator input decreases after reaching the threshold and the voltage comparator input increases after reaching the low level threshold. Further, when the drive voltage does not change within a predetermined time, the drive voltage is forcibly switched, and the oscillation period is set between the two coils or two capacitors to be compared with the predetermined time as the maximum half cycle. A self-excited oscillation circuit that is inversely proportional to the constant difference is constructed, and the identification control unit identifies the constant difference between the two coils or two capacitors to be compared from the period of the pulse train. Detection circuit 2. The minute difference detection circuit of two circuit elements according to claim 1, further comprising a first integration circuit, wherein the signal proportional to the detection potential difference is a first integration voltage obtained by integrating the detection potential difference, One integration circuit integrates the detected potential difference corresponding to the excessive current flowing through the RLC circuit after the drive voltage is switched by the energization control unit, and the voltage comparator having a hysteresis characteristic has the first integration voltage at a high level and a low level. When the level threshold is reached, the output level is switched, and the energization control unit integrates and subtracts the detected potential difference after the first integrated voltage reaches the high level threshold, and integrates and adds the detected potential difference after the low level threshold is reached. The driving voltage applied to the RLC circuit is switched, and if the driving voltage does not change within a predetermined time, the driving voltage is forcibly switched, and the predetermined time is set as the maximum half cycle. A self-excited oscillation circuit that makes the cycle inversely proportional to the constant difference between the two coils or two capacitors to be compared and the identification control unit determines the constant difference between the two coils or two capacitors to be compared from the cycle of the pulse train. 2 circuit element minute difference detection circuit characterized by distinguishing 2. The minute difference detection circuit of two circuit elements according to claim 1, further comprising a first integration circuit and a second integration circuit, wherein a signal proportional to the detection potential difference is obtained by second-order integration of the detection potential difference. The first integrating circuit integrates the detected potential difference corresponding to the excessive current flowing through the RLC circuit after the drive voltage is switched by the energization control unit, and the second integrating circuit is the first integrating circuit. The difference between the output of the circuit and the reference potential is integrated to obtain a second integrated voltage proportional to the constant difference between the two coils or two capacitors to be compared, and the voltage comparator with hysteresis characteristics is the second integrated voltage. When the voltage reaches the high and low level thresholds, the output level is switched, and the energization control unit integrates and subtracts the detected potential difference after the second integrated voltage reaches the high level threshold, and after reaching the low level threshold, the detected potential difference. But The drive voltage applied to the RLC circuit is switched so as to be added, and if the drive voltage does not change within a predetermined time, the drive voltage is forcibly switched, and the oscillation period is set to the predetermined half time as the maximum half cycle. A self-excited oscillation circuit is constructed that is inversely proportional to the constant difference between the two coils or two capacitors to be compared, and the identification control unit identifies the constant difference between the two coils or two capacitors to be compared from the period of the pulse train Two circuit element minute difference detection circuit 4. The minute difference detection circuit of two circuit elements according to claim 1, 2 or 3, wherein the identification control unit directly or counts down the period of the pulse train and then compares two coils or two capacitors to be compared by minute interval pulse counting. A small difference detection circuit of two circuit elements characterized by identifying a constant difference between them 4. A minute difference detection circuit for two circuit elements according to claim 1, 2 or 3, wherein the first or second driving voltage is applied to the RLC circuit at the rising or falling edge of the output of the voltage comparator. A small difference detection circuit for two circuit elements characterized by distinguishing the magnitude relation between the two circuit elements from the type of the circuit 4. The minute difference detection circuit for two circuit elements according to claim 1, 2 or 3, wherein an RLC circuit for comparing two coils comprises a bridge composed of two resistors and two coils. A minute difference detection circuit of two circuit elements characterized by outputting a detection potential difference corresponding to a constant difference between the two circuit elements 4. The minute difference detection circuit for two circuit elements according to claim 1, 2 or 3, wherein the RLC circuit for comparing the two coils is based on the serial connection of the two coils, and a resistor is further inserted in series. Two circuit elements characterized in that a resistance is connected in parallel to the coil of the coil, and the detected potential difference is a potential difference between the midpoint equivalent potential between the two coils and the time average potential of the midpoint equivalent portion potential. Minute difference detection circuit 4. The minute difference detection circuit for two circuit elements according to claim 1, 2 or 3, wherein an RLC circuit for comparing two capacitors comprises a bridge composed of two resistors and two capacitors. A minute difference detection circuit of two circuit elements characterized by outputting a detection potential difference corresponding to a constant difference between the two circuit elements 4. The minute difference detection circuit for two circuit elements according to claim 1, 2 or 3, wherein an RLC circuit for comparing two capacitors is based on a series connection of two capacitors and a resistor is further inserted in series. And a detection potential difference between the two capacitors, the difference between the midpoint equivalent portion potential and the time average potential of the midpoint equivalent portion potential. 4. The small difference detection of two circuit elements according to claim 1, 2 or 3, wherein two coils whose at least one coil constant varies depending on a position of a movable body made of a magnetic body or a conductor and the two coils are compared. A position detection device comprising a circuit and detecting a position of a movable body by identifying a constant difference between the two coils 11. The position detecting device according to claim 10, wherein one coil is a reference coil having a constant inductance, and when the inductance of the other coil increases, the inductance difference between the two coils increases, and conversely, when the inductance decreases, the inductance difference between the two coils increases. An RLC circuit including two coils is set so as to decrease, and the proximity of the magnetic body and the conductor is detected with high sensitivity by compensating for the inductance change that increases or decreases due to the proximity of the magnetic body or the conductor. 4. A detection unit including two coils, scanning means for relatively moving and scanning an object including a magnetic substance or a conductor, and a detection unit, and a minute difference detection circuit for two circuit elements according to claim 1, 2 or 3 The scanning means moves and scans the subject relative to the detection unit while placing the subject in the magnetic field generated by the two coils, and the minute difference detection circuit of the two circuit elements has a minute inductance between the two coils. Inspection apparatus characterized by identifying and detecting defects or presence / absence of magnetic material or conductor by referring to each other's coils by detecting difference

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