JP2003207367A - Position sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose an inductance sensing circuit high in accuracy despite its simplified structure for the embodiment of a low cost position sensor. <P>SOLUTION: The position sensor has two coils and a magnetic body or a conductor whose position relative to at least one of the coils is changed for a change in inductance; an emitter coupled oscillation circuit wherein the coils are connected as loads to the collectors of two transistors with the collectors directly cross-coupled to the bases and with the emitters coupled by a capacitor, or an oscillation circuit which is a hysteresis equipped inverting amplifier having two circuits between the input and output ends, wherein coils and diodes connected in series with the diode directions inverted are connected in parallel, with capacitors connected to the input and output ends; or the like. The sensor senses a position by grasping changes in inductance as pulse outputs different in duty ratio. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a position detector,
In particular, it relates to a position detector that detects the position of a magnetic body or conductor whose inductance changes depending on the mutual positional relationship with the coil with a simple circuit.

[0002]

2. Description of the Related Art Position detectors include devices based on various principles depending on the application, but as a position detector that can be used in a high temperature or severely contaminated environment, a position detector that detects an inductance change due to an eddy current effect The vessel is suitable.

Conductors close to the inside and outside of the solenoid coil,
It is possible to know the position of the conductor and the magnetic body by changing the inductance of the coil by changing the inductance of the coil depending on the mutual relation between the magnetic body and the coil or the mutual relation between the planar coil and the conductor and the magnetic body. However, there are various problems when trying to improve the accuracy.

In many conventional examples, an inductance change is detected from a voltage or a voltage waveform change between coil terminals by applying an AC sine wave voltage or a rectangular wave voltage to a series circuit of a coil and a resistor. . In this case, the resistance of the coil wire and the loss when the coil is excited by high frequency are likely to change depending on the temperature, resulting in lowering the position detection accuracy.

Another important problem is the large number of analog circuit parts in the detection circuit, and the large number of adjustment points such as voltage and resistance, which impairs detection accuracy other than the structure of the detection part and increases the cost. Has become. As an example in which the detection circuit can be made relatively simple, attention is paid to US Pat. No. 4,644,570.
No. 05-040002 and 05-1104
12, a detection circuit to which the self-excited oscillation circuit of Japanese Patent Laid-Open No. 2000-321009 is applied. Although the specific oscillation circuit in US Pat. No. 4,644,570 is unknown, the circuit is complicated even if the intention to improve the resolution by using a digital circuit is good, and there is a time delay in detection. JP-A-0
Although 5-040002 and Japanese Patent Laid-Open No. 05-110412 use a simple oscillation circuit, temperature fluctuations are not taken into consideration by position detection with a single coil, and the operation or stability of the oscillation circuit is not considered. Doubt remains. JP 2000-3
The 21009 has the advantage of being able to detect the inductance differentially, but there are many parts and the stability of the circuit operation remains questionable. Due to various reasons, the detection circuit of the self-oscillation circuit type has not been widely applied although it has a possibility.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to propose an inductance detecting circuit having a simple structure while ensuring accuracy, and to realize and provide a low cost position detector.

[0007]

A position detector according to the present invention comprises two coils, a magnetic material or a conductor for changing the inductance depending on the mutual positional relationship with at least one of the coils, and the two coils are capacitors. An oscillation circuit that outputs a pulse train having a duty ratio proportional to the time ratio required for charging and discharging, and a duty ratio identifying means for the pulse train, and the relative position of the magnetic body or conductor and the coil is determined from the duty ratio of the pulse train. It is characterized by detecting.

As a concrete circuit of the oscillation circuit, the oscillation circuit has two coils as loads at the collector terminals thereof, and the collector terminals of the two transistors are directly cross-coupled to their respective base terminals. We propose an emitter-coupled oscillating circuit that is configured by coupling capacitors with each other.

As still another specific circuit, a coil and a diode are connected in series and two sets of circuits in which the directions of the diodes are reversed are provided in parallel between the input and output ends, and the capacitor is connected to the input end. We have proposed an oscillator circuit consisting of an inverting amplifier with hysteresis characteristics.

A concrete circuit of the duty ratio identifying means is as follows.
The simplest is a circuit that obtains a difference in duty ratio as a voltage difference by an integrating circuit using a resistor and a capacitor or a low-pass filter. However, as a recent technical trend, measured values are often digitized and processed by a microcomputer, and usually an A / D converter is arranged after the integrating circuit to digitize the measured values. The position detector according to the present invention also proposes a method in which a pulse train whose duty ratio changes is directly input to a microcomputer and an internal timer or counter directly counts and detects the pulse interval and the pulse duty ratio.

Regarding the two coils, in relation to a moving conductor or a magnetic body, it is basically necessary to secure high accuracy as a differential structure in which one increases the inductance and the other decreases, but one of them is a reference coil. As a fixed inductance, we also proposed a configuration in which the coil on the fixed inductance side is replaced with a resistor, and miniaturization is prioritized at the expense of some accuracy.

[0012]

Since the detection circuit of the present invention is based on a self-excited oscillation circuit that charges and discharges one capacitor via two coils respectively, the high-level and low-level time widths in the output pulse train are different. It is proportional to the inductance of the coil. Even if the capacitance of the capacitor fluctuates and the cycle of the output pulse fluctuates, it does not affect the duty ratio, and the duty ratio within the pulse train has few influencing factors other than the coil, so the detection circuit functions without adjustment. Since the position is detected by the difference between the inductances of the two coils, in-phase fluctuations such as power supply fluctuations and temperature fluctuations can be compensated. Further, it is possible to simplify the position detector by using one coil as a fixed inductance coil or a resistor.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments and principles of the position detector according to the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the structure of a detector for detecting the position of a moving body whose position relative to the coil changes. In FIG. 1A, the coils 13 and 14 are wound around a non-magnetic support 15 and made of resin.
1 is arranged on the outer periphery of the coils 13 and 14 and is configured to move together with the moving body. The conductor portion 12 is a metal thin film, a metal plating film, or the like, and is arranged on the inner peripheral surface of the cylinder 11.

When the conductor portion 12 moves to the left and right along with the cylinder 11, the lengths A and B of the overlapping portions of the coils 13 and 14 and the conductor portion 12 change, and the coils 12 and 13 respectively.
The inductance of changes. Two coils 13, 14
Since the inductance of is increased when one is increased, the other is decreased, so that the detection circuit can detect the position with high accuracy by differentially detecting the amount of change. In addition to the conductor, the conductor portion 12 may be made of a magnetic material such as ferrite or permalloy. In the case of a conductor, the inductance of each coil is inversely proportional to the overlapping lengths A and B because of the eddy current effect on the conductor surface. In the case of a magnetic body, since the magnetic resistance changes due to the magnetic permeability of the magnetic body, the inductance of each coil changes in proportion to the lengths A and B.

In contrast to FIG. 1A, the shaft 16 arranged in the coils 13 and 14 is fixed to the moving body in FIG. 1B.
This is an example in which a conductor portion 17 made of a conductor ring is arranged on the surface of the shaft 16. The operating principle is the same as in FIG.

Although the structure of the detecting portion of the position detector shown in FIGS. 1A and 1B is generally known, various problems remain in the circuit for detecting the change in inductance. The present invention proposes a new detection circuit for detecting a change in inductance. Before explaining the embodiment of the present invention, an example of a conventional detection circuit will be reviewed and its problem will be clarified. FIG. 10 shows a simplified detection circuit which is generally used. In the figure, coils 13 and 14 and resistors 101 and 1
A high-frequency signal is applied from the high-frequency oscillator 103 to the bridge constituted by 02, and the resistors 101, 102 and the coil 13,
The voltage divided by 14 and the rectifying / smoothing circuit 10 respectively.
A direct current voltage is converted at 4, 105, and a differential output is obtained at the differential amplifier 106. The voltage across the coils 13 and 14 is adjusted by the rectifying / smoothing circuit 10 by the differential amplifier 106.
4 and 105, there is some adjustment unit to maintain these gain balances, and the high frequency oscillator 1
03 is required separately, and its output must be strictly controlled.

FIG. 2 shows a detection circuit of the position detector which is the first embodiment of the present invention. It uses an emitter-coupled oscillator circuit and detects the position by directly identifying the duty ratio of the output pulse train with a microcomputer. In the figure, the coils 13 and 14 are connected to the collector terminals as loads of the transistors 22 and 23.
The collector terminals of 23 are transistors 23 and 22 respectively.
And a capacitor 21 is connected between the emitter terminals of the transistors 22 and 23. The resistors 24 and 25 determine the current when the transistors 22 and 23 are on. Reference numeral 26 is a waveform shaping comparator, and reference numeral 27 is a microcomputer.

Although the state when the power is turned on is indefinite, considering that the transistor 22 has turned on, the current flows in the coil 1
3, the current flows through the transistor 22 and the resistor 24, and further branches into the capacitor 21 and the resistor 25. Resistor 25 at this point
, The emitter potential of the transistor 23 is sufficiently high, the transistor 23 is turned off, the collector of the transistor 23 and the base of the transistor 22 are at high level, and the transistor 22 is kept on.
When the charge storage in the capacitor 21 becomes large, the capacitor 2
The current flowing through the resistor 25 through 1 gradually decreases, and the emitter potential of the transistor 23 gradually decreases. The base of the transistor 23 is connected to the collector of the transistor 22, and when the potential difference from the emitter of the transistor 23 reaches a predetermined level, the transistor 23 turns on and its collector terminal voltage decreases, so the transistor 22 turns off. The current flowing through the coil 14 is the transistor 2
3 flows through the resistor 25, but partly the capacitor 21 and the resistor 2
4 to charge the capacitor 21 from the opposite direction. In this way, the capacitor 21 is alternately charged from the opposite direction through the coils 13 and 14 to continue the self-excited oscillation.

When the level difference between the collector terminals of the transistors 22 and 23 is pulse-shaped by the comparator 26, the durations of the high level and the low level are coil 13, respectively.
It is proportional to the time constant determined by 14 and the capacitor 21. This output is input to the microcomputer 27, and the duty ratio is calculated from the ratio of the high level time width and cycle to calculate the torque. If you sacrifice a little accuracy, you can simply calculate the torque from the difference between the high-level time width and the low-level time width.

In the oscillating circuit, the resistors 24 and 25 set the current values flowing through the transistors 22 and 23, and the time width of the output pulse train is related only to the inductance of the coils 13 and 14 and the capacitor 31. Little impact. Although the capacitance of the capacitor 31 in the detection circuit may be affected by temperature and the oscillation cycle may be changed, it does not affect the pulse duty ratio. Further, recently, there are many cases where digital processing is performed, so the output pulse train is directly input to the microcomputer 27 for time discrimination to be digitized, but at this stage, the influence of the power supply voltage and other fluctuation factors is small.

Further, the collector terminals of the transistors 22 and 23 are directly cross-coupled to the base terminals of the transistors 23 and 22, but the collector terminals of the transistors 22 and 23 are respectively provided with emitter follower circuits, and the outputs of the emitter follower circuits to the transistors 23 and 22. It may be connected to each of the base terminals of 22 and can contribute to stabilization of the oscillation operation.

FIG. 3 shows an output pulse train in the first embodiment, and the description of the first embodiment will be supplemented with reference to the drawing. The horizontal axis 31 indicates time, and FIGS. 3A and 3B are output pulse trains 32 and 33 of the comparator 26 of FIG. 2, respectively.
Indicates. The high-level and low-level time widths of the output pulse trains 32 and 33 are controlled by the capacitors 2 through the coils 13 and 14.
Since it is proportional to the charging time of 1, the inductance difference is obtained from the difference between the high-level time width and the low-level time width, and the torque can be calculated. The output pulse trains 32 and 33 have the same duty ratio T1 / (T1 + T2), but the pulse cycle (T
1 + T2) indicates different states. This may occur when the inductances of the coils 13 and 14 both change due to a difference between detectors or a temperature change.

FIG. 3C is a diagram for explaining a method of measuring the high-level time width T1, the low-level time width T2, etc. by the microcomputer 27. The microcomputer 27 inputs the output pulse train 33 and measures the time with a built-in counter or program. The high-level time width T1 and the low-level time width T2 are counted and measured by the pulse train 34 having a sufficiently small time interval. Specific methods include a method using a counter built in the microcomputer and a method of counting the number of times the program step corresponding to the pulse interval time of the pulse train 34 is repeated. The number of pulses may be counted using a counter circuit instead of the microcomputer.

The inductances of the coils 13 and 14 decrease when one increases and the other decreases. Therefore, the pulse period of the output pulse can be approximately constant by appropriately setting the circuit constant. However, the coil 13 shown in FIGS.
Depending on the specific structure, material, etc., of the detection unit consisting of 14, etc., the expansion and contraction of the coils 13, 14 will become asymmetric due to temperature fluctuations, or eddy current loss will occur when high-frequency current is applied to the coils 13, 14. The inductance of the coils 13 and 14 may increase or decrease with a change in temperature because of a change in balance. Utilizing this, it is possible to monitor the cycle of the oscillation output pulse train and detect the temperature change of the detector, and it is also possible to correct the calculated position by knowing the cycle of the output pulse from the data collected and stored in advance. It is possible. In that respect, the method of calculating the position by knowing the high-level time width and pulse period by the microcomputer can also correct the influence of the temperature and realize higher accuracy. However, in that case, since the capacitor 21 may be affected by the temperature fluctuation and may affect the pulse period, it is necessary to use a capacitor element that is not easily affected by the temperature fluctuation and pay attention to constant temperature.

FIG. 4 is a flowchart showing an example of a program for calculating the position by detecting the inductance difference by the microcomputer 27.

[1. ], [2. ] Step,
A high-level time width T1 and a low-level time width T2 are obtained from the output of the comparator 26 using a counter in the microcomputer 27. [3. ] High level time width T
1 is compared and verified with the previous value, and if the difference is equal to or greater than a predetermined value, it is determined as abnormal [7. ], It is regarded as normal if it is less than a predetermined value [4. ] Step.
[4. ] Compares the detected low-level time width T2 with the previous value, and if the difference is equal to or greater than a predetermined value, it is regarded as abnormal [7. ], And if it is less than a predetermined value, it is regarded as normal [5. ] Step.

[5. ] In (T1-T2) / (T1 + T
The position is calculated from 2), and [6. ], The correction data of the calculated position is obtained from the database using T1 + T2 related to the pulse period as an index and corrected [1. ] To continue the measurement.
The position may be calculated as T1 / (T1 + T2) instead of (T1-T2) / (T1 + T2). If the accuracy may be sacrificed a little, it can be simply calculated from T1-T2.

[7. ] Is the high-low level time width T1, T2
Is an abnormal processing routine, comparing and verifying T1 and T2 with the past history, and checking the frequency and continuity of the abnormal state from the past change history to determine whether it is an accidental error or a fixed error. If the error is probabilistic and infrequent, it is judged to be random [1. ] And repeat the measurement. If the error frequency is high and the continuity is high, it is regarded as a fixed failure [8. ] To alert the host system and stop the measurement work.

As shown in FIGS. 2, 3 and 4, according to the first embodiment of the present invention, there is almost no analog circuit portion,
Since the measurement can be performed by digital processing, the detection circuit can function without adjustment, and it is possible to judge the abnormality of the detector.

FIG. 5 shows a detection circuit of a position detector which is a second embodiment of the present invention. In the figure, numeral 58 indicates an oscillator circuit, and numeral 59 indicates an integrating circuit. The oscillator circuit 58 includes coils 13 and 14 and diodes 52 and 5 respectively.
3 is connected in series and is connected in parallel to the input / output terminal of the inverting amplifier 54, and the capacitor 51 is connected to the input terminal of the inverting amplifier 54. The other end of the capacitor 51 is grounded to facilitate shielding including the circuit. In that case, the diodes 52 and 53 are connected in opposite directions, and the inverting amplifier 54 has a hysteresis characteristic. Integration circuit 5
Reference numeral 9 is simply composed of a resistor 55 and a capacitor 56.

It is assumed that the output of the inverting amplifier 54 becomes high level when the input terminal becomes lower than the first level, and becomes low level when the input terminal becomes larger than the second level. When the input terminal is now lower than the first level, the output becomes high level, and the current flows through the diode 53 and the coil 14 to the capacitor 5
1 is charged, and when the voltage of the capacitor 51 rises and exceeds the second level, the output of the inverting amplifier 54 shifts to a low level, and the capacitor 5 passes through the coil 13 and the diode 52.
The electric charge of 1 is discharged. The voltage of the capacitor 51 gradually decreases, and when it falls below the first level, the output of the inverting amplifier 54 turns to a high level and repeats this.

Since the charging of the capacitor 51 depends on the time constant of the coil 14 and the capacitor 51 and the discharging depends on the time constant of the coil 13 and the capacitor 51, the high level time width of the output pulse train is the inductance of the coil 14 and the low level time width. Is proportional to the inductance of the coil 13. The integrator 59 smoothes the output pulse train by the resistor 55 and the capacitor 56 to output the DC voltage 5 proportional to the duty ratio from the pulse train having different duty ratios.
Get 7.

Also in the second embodiment, the time widths of the high and low levels of the output pulse train are the coils 14 and 13 and the capacitor 5, respectively.
There is little room for other factors to influence it. The capacity of the capacitor 51 may be affected by temperature fluctuations, but since it contributes equally to the time width of high and low levels, it affects the oscillation cycle but does not affect the duty ratio. However, since the inverting amplifier 54 is generally asymmetric in the driving method for high and low output levels, there is a possibility that high and low pulse widths may have asymmetry due to the influence of temperature fluctuations. It is necessary to use properly. Further, since the integrating circuit 59 outputs the voltage, the level of the pulse input to the integrating circuit 59 must be strictly controlled. This can be improved by arranging a pulse shaping circuit before inputting to the integrating circuit 59. The integrating circuit 59 uses a simple circuit in consideration of cost, but if it is replaced with a low-pass filter capable of sufficiently attenuating a high frequency region, an output voltage with less ripple can be obtained.

FIG. 6 shows a third embodiment of the present invention, in which a finite rotation angle is detected. In the figure (a),
The rotating shaft 62 has a fan-shaped conductor 61 fixed and rotates in a finite angle range, and print coils 64 and 65 are arranged and fixed on the surface of a fixed portion 66 so as to face the fan-shaped conductor 61.
The number 63 indicates the moving direction of the fan-shaped conductor 61. As shown in FIG. 6B, the two printing coils 64 and 65 are symmetrically formed as spiral coils by thin film technology such as plating and etching.

If the circumferential length of the fan-shaped conductor 61 is substantially equal to the circumferential length of each of the printing coils 64 and 65, and the lengths of the portions overlapping the printing coils 64 and 65 are A and B, respectively. The inductance of changes differentially according to A and B. In FIG. 6A, the detection circuit shown in the second embodiment of the present invention is connected and shown.
The voltage appearing at the output 57 changes corresponding to the lengths of A and B, and the rotation angle of the rotation shaft 62 can be detected.

In the third embodiment, an example of detecting the angle of the rotating shaft has been shown. However, the position detection of the conductor piece or the magnetic piece moving parallel to the printing coils 64 and 65 shown in FIG. 6B is detected. Of course it can be applied.

In the first, second and third embodiments of the present invention, an example in which the moving body can differentially change the inductances of the two coils can be accurately detected by a simple detection circuit is shown. Even when there is no room to arrange the two coils, there are many in practical use. In that case also, in the detection circuits described in the first and second embodiments of the present invention, one of the coils may be replaced with a coil having a fixed inductance or a position detector having a single detection coil instead of a resistor. Applicable.

However, in that case, the accuracy is often impaired due to the fluctuation of the resistance of the detection coil due to the temperature fluctuation or the fluctuation of the physical constants of the conductor, the magnetic body and the like facing the detection coil. An example in which the accuracy is not impaired as much as possible even in the case of such a single detection coil will be described as the fourth and fifth embodiments of the present invention with reference to FIGS. 7, 8 and 9.

FIG. 7 shows a fourth embodiment of the present invention in which one of the differential coils has a fixed inductance. In the figure, a detection coil 72 and a reference coil 73 wound around a support 74 are arranged in a cylinder 71 fixed to a moving body. As the second embodiment, the circuit shown in FIG. 5 is applied to the detection circuit.

In the figure, the cylinder 71 is a conductor, and the detection coil 72 has a length C that overlaps in the moving range.
, But the reference coil 73 always overlaps with the cylinder 71. The reference coil 73 uses a conductive wire thinner than the detection coil 72 to reduce its occupied area, and temperature compensation is performed by setting the temperature coefficients of the electric resistance components of the detection coil 72 and the reference coil 73 as equal as possible.

The important role of the reference coil 73 is to compensate the temperature variation of the detection coil 72 as much as possible. However, if this point can be relaxed, it is not limited to the position shown in FIG. Can do In the example shown in FIG. 7, the edge portion of the cylinder 71 does not exist in the reference coil 73, but when the effect of the edge portion is canceled by differential, the arrangement is changed and the reference coil 73 is equivalent to the cylinder 71. The structure may be such that the edge portions of the conductor are arranged.

The oscillation circuit portion of the detection circuit is the same as that of the second embodiment shown in FIG. 5, but the microcomputer 75 is arranged to identify the duty ratio of the output pulse. Since the waveform of the output pulse train in FIG. 7 is the same as that in FIG. 3 referred to in the first embodiment, an example of the program flow in the microcomputer in FIG. 7 will be described with reference to FIGS. 3 and 8. Since the reference coil 73 is related to the time for charging the capacitor 51, the high level time width T1 in FIG. 3 is proportional to the inductance of the reference coil 73, and the low level pulse width T2 is proportional to the inductance of the detection coil 72. Therefore, the example program flow is as follows.

[1. ], [2. ] Step,
A high level time width T1 and a low level time width T2 are obtained by using a counter in the microcomputer 75.
[3. ], The high-level time width T1 is compared and verified with the previous value, and if the difference is equal to or larger than a predetermined value, it is determined as abnormal [7. ], It is regarded as normal if it is less than a predetermined value [4. ] Step. [4. ] Compares the detected low-level time width T2 with the previous value, and if the difference is equal to or greater than a predetermined value, it is regarded as abnormal [7. ], And if it is less than a predetermined value, it is regarded as normal [5. ] Step.

[5. ] In (T2-T1) / (T1 + T
The position is calculated from 2), and [6. ] High level time width T
The correction data of the calculated position is obtained from the database using 1 as an index and corrected [1. ] To continue the measurement. Since T1 should ideally not fluctuate, it is used as a temperature detecting means of the detecting unit, and unbalanced fluctuations caused by temperature are collected in advance and corrected from the stored database.

[7. ] Is the high-low level time width T1, T2
Is an abnormal processing routine, comparing and verifying T1 and T2 with the past history, and checking the frequency and continuity of the abnormal state from the past change history to determine whether it is an accidental error or a fixed error. If the error is probabilistic and the frequency is low, it is judged to be random [1. ] And repeat the measurement. If the error frequency is high and the continuity is high, it is regarded as a fixed failure [8. ] To alert the host system and stop the measurement work.

FIG. 9 shows a fifth embodiment of the present invention. The reference coil 73 in the fourth embodiment is replaced with the resistor 91 and arranged in the detection coil 72. The detection circuit employs the second embodiment shown in FIG. The charging of the capacitor 51 depends on the time constant determined by the capacitor 51 and the resistor 91, and the discharging depends on the time constant determined by the capacitor 51 and the inductance of the detection coil 72. By matching the temperature coefficient of the resistance component of the detection coil 72 and the temperature coefficient of the resistance 91, temperature compensation for position detection becomes possible. Further, as shown in FIG. 7, if the duty ratio of the pulse train is identified by the microcomputer 75, temperature information can be obtained from the variation of the resistance 91, and accurate temperature correction can be performed.

In a position detector using a single detection coil, a method of changing the frequency of a self-excited oscillator by using an inductance has been proposed, but a means for converting the frequency into a voltage is required and many analog circuit parts are required. ， There is a drawback that adjustment points remain. In addition, there is a drawback that a separate circuit is required for compensating for temperature fluctuations in the detection coil portion, resulting in a complicated circuit. Even in such a case, the fifth embodiment shown in FIG. 9 can realize a position detector which includes a temperature compensating means and has a simple circuit and which requires almost no adjustment points.

[0049]

As described in the above embodiments, according to the position detector of the present invention, the basis of the inductance detecting circuit is to output a pulse train having a duty ratio proportional to the time when the two coils charge and discharge the capacitors. As a self-oscillation circuit,
The duty ratio can be output as a voltage by a simple circuit or directly input to the microcomputer for identification. There are very few factors other than the two coils that affect the duty ratio of the output of the oscillation circuit, and the detection circuit functions with almost no adjustment, and a simple detection circuit can realize low cost and high accuracy.

In addition to the examples shown in the embodiments, the position detector of the present invention can be applied to magnetic bearing devices and various control systems. Further, the present invention is broadly understood, and various detection devices such as a magnetic flaw detection device by an inductance change,
It can be widely applied to metal piece detection devices.

[Brief description of drawings]

FIG. 1 is a sectional view of a position detection unit having a differential coil configuration.

FIG. 2 is a detection circuit according to the first embodiment of the present invention.

FIG. 3 is an output pulse train in the first embodiment.

FIG. 4 is a program flow chart in the first embodiment of the present invention.

FIG. 5 is a detection circuit according to a second embodiment of the present invention.

FIG. 6 is a third embodiment of the present invention.

FIG. 7 is a fourth embodiment of the present invention.

FIG. 8 is a program flow chart according to a fourth embodiment of the present invention.

FIG. 9 is a fifth embodiment of the present invention.

FIG. 10: Conventionally proposed bridge-type detection circuit

[Explanation of symbols]

11 ... Cylinder, 12 ... Conductor, 13, 14 ... Coil, 15 ... Support, 16 ... Shaft, 17 ...
Conductor part, 21 ... Capacitor, 22, 2
3 ... Transistor, 24, 25 ... Resistance,
26 ... Comparator, 27 ... Microcomputer, 31 ... Time, 32,
33 ... Output pulse train, 34 ... Pulse train with small time interval, 51 ... Capacitor, 52, 5
3 ... Diode, 54 ... Inverting amplifier,
55 ... Resistor, 56 ... Capacitor,
57 ... Output, 58 ... Oscillation circuit,
59 ... Integrator circuit, 61 ... Fan-shaped conductor,
62 ... rotation axis, 63 ... movement direction,
64, 65 ... Printing coil, 66 ... Fixed part, 71 ... Cylinder, 72 ... Detection coil, 73 ... Reference coil, 74 ...
..Supports, 75 ... Microcomputers, 91 ..
..Resistance, 101, 102 .... Resistance, 103
..High-frequency oscillators, 104, 105..Rectifying / smoothing circuits, 106 ... Differential amplifiers

Claims (11)

[Claims] 1. Two coils, a magnetic material or a conductor that changes the mutual positional relationship with at least one of the coils to change the inductance, and the two coils are proportional to the time ratio required to charge and discharge the capacitor. The pulse train is composed of an oscillation circuit for outputting a pulse train having a duty ratio, and a duty ratio discriminating unit for the pulse train, which is composed of a counting unit for counting the pulse width at a minute time interval or an integrating circuit
A position detector characterized by detecting the relative position of a magnetic body or conductor and a coil from the duty ratio of the pulse train. 2. The position detector according to claim 1, wherein the oscillation circuit has two coils as loads at the collector terminals, and two transistors having the respective collector terminals cross-coupled to each other's base terminals. Position-detector characterized by being an emitter-coupled oscillator circuit configured by coupling the emitters of each other with a capacitor 3. The position detector according to claim 1, wherein a coil and a diode are connected in series, and two sets of circuits in which the directions of the diodes are opposite to each other are provided in parallel between the input and output ends, and a capacitor is provided. Position detector characterized by oscillating circuit composed of inverting amplifier with hysteresis characteristic connected to input terminal 4. The position detector according to any one of claims 1 to 3, wherein the inductance of the first coil increases and the inductance of the second coil increases in proportion to the relative position between the two coils and a magnetic body or a conductor. Position detector characterized in that the inductance is configured to decrease 5. The position detector according to claim 4, wherein the relative position between the magnetic body or the conductor and the coil detected by the duty ratio identifying means of the pulse train is obtained by obtaining temperature information from the repeating interval of the output pulse. Position detector characterized by 6. The position detector according to any one of claims 1 to 3, wherein the inductance of the first coil changes in proportion to the relative position fluctuation with respect to the magnetic substance or the conductor, but the second coil has the first coil. Position detector characterized in that it is substantially equivalent to a coil and has a constant inductance 7. The position detector according to claim 6, wherein the second coil is arranged in substantially the same environment as the first coil. 8. The position detector according to claim 7, wherein the temperature information is obtained from the output pulse width resulting from the inductance of the second coil, and the magnetic substance or conductor is detected by the duty ratio identifying means of the pulse train. Position detector characterized by correcting the relative position to the coil 9. The position detector according to claim 6, wherein a resistor is used instead of the second coil. 10. The position detector according to claim 9, wherein:
The position detector characterized in that the resistance has a temperature coefficient substantially equal to that of the first coil resistance and is arranged in substantially the same environment as the first coil. 11. The position detector according to claim 10, wherein temperature information is obtained from an output pulse width caused by the resistance, and relative to a coil or a magnetic substance or conductor detected by a duty ratio identifying means of a pulse train. Position detector characterized by correcting position