JP2001147102A - Position detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detector having the minimized whole length and magnitude of the diameter direction relative to a detection distance, and capable of being manufactured easily. SOLUTION: This position detector for detecting a linear position change by using a coil is so composed that an electric conductor 5 or a magnetic material 6 is moved on the inner diameter side of the coil 3 or a tubular electric conductor 7 or a magnetic material 8 is moved on the outer diameter side of the coil 3 to thereby change the inductance of the coil 3 and to change the combined impedance of the coil 3 and a resistance 4, and that, by utilizing the change of times of charge and discharge to/from a capacitor 1 caused by these changes, the frequency of oscillation by using a comparator 2 is changed and the frequency is observed to thereby detect the positions of the electric conductors 5, 7 or the magnetic materials 6, 8 moving on the inner diameter side or the outer diameter side of the coil 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a voltage corresponding to a displacement,
Alternatively, the present invention relates to a position detector which outputs a current or detects displacement to determine whether or not it is at a predetermined position and generates a switch output.

[0002]

2. Description of the Related Art In a conventional position detector, a differential transformer as shown in FIG. 2 is used, and one excitation coil (15) is used.
And two detection coils (16) (1
7) and a magnetic body (18), three coils (15), (16) and (17) are arranged on the same axis, and the magnetic body (18) is inserted inside the coil. Excitation coil (1
5) is excited by a sine wave to generate a magnetic field and concentrate the magnetic flux on the magnetic body (18). As a result, the detection coils (16) and (17) generate a voltage by electromagnetic induction.
Since the two detection coils (16) and (17) are differentially connected, the difference between the induced electromotive forces of the respective detection coils (16) and (17) is output depending on the insertion position of the magnetic body (18). . The relationship between the displacement amount of the magnetic body (18) and the output voltage is as shown in FIG. 3, and when the magnetic body (18) is displaced over the entire length of the two detection coils (16) and (17), the same output voltage is converted into two values. Therefore, the practical detection range is 2
The length in the axial direction corresponds to one of the detection coils (16) and (17).

[0003]

In a differential transformer, two detection coils (16) (1) arranged in the axial direction are provided.
7), the total length must be at least 2 times the detection distance.
Requires twice the length. Also, three coils (15) (1
6) Since (17) is required, it is not suitable for miniaturization. In particular, as shown in FIG. 4, when mounted on the hydraulic cylinder (19), the total length of the differential transformer (20) needs to be at least twice as long as the cylinder displacement (21). It cannot be completely housed inside, and the differential transformer pops out, requiring more space for installation. Further, two connection cables are required for the excitation coil and two connection cables for the detection coil, which is disadvantageous in manufacturing and miniaturization. Also,
Generally, the structure of the differential transformer is a structure in which the magnetic body (23) is moved at the inner diameter of the coil, and the piston rod (2) is moved.
A structure for joining in 2) and a structure for incorporating the coil in a hollow pressure-resistant container are required, which is disadvantageous in manufacturing and miniaturization.

It is an object of the present invention to provide a position detector which minimizes the total length of the position detector with respect to the detection distance, minimizes the size in the radial direction, and is easy to manufacture.

[0005]

To achieve the above object, a position detector according to the present invention comprises a coil, a rod-shaped or pipe-shaped conductor or a magnetic body, a displacement detector, and a resistor. , An oscillation circuit unit including a capacitor and a comparator, a frequency-voltage conversion unit, and an output conversion unit.

[0006] The coil used in the displacement detector is a single conductive wire wound in a cylindrical shape. When detecting displacement at the inner diameter of the coil, the coil is an air-core coil, and detecting displacement at the outer diameter of the coil. In this case, an air-core coil or a cored coil having a rod-shaped magnetic material as a core is used.

[0007] The conductor or magnetic material used for the displacement detecting section is rod-shaped or pipe-shaped, and is joined to or integrally formed with an object to be detected.

The resistor used in the oscillation circuit is connected in series with the coil, and one of the resistors is connected to the comparator input side.
The other is connected to the comparator output.

In the capacitor used in the oscillation circuit section, one pole is connected to 0 V (volt) and the other pole is connected to the input side of the comparator.

[0010] The comparator used in the oscillation circuit section is
This is an inverting output comparator with a threshold with hysteresis. When the input voltage rises from a low voltage, it is determined by the threshold on the high voltage side, and when the input voltage exceeds the threshold, a low level is output. Thereafter, when the input voltage falls from the high voltage side, it is determined by the threshold value on the low voltage side, and when the input voltage exceeds the threshold value, a high level is output. Specifically, in addition to the comparator, an operational amplifier, a Schmitt inverter of a logic element, or the like can be used.

The frequency-voltage converter observes the output oscillated by the comparator and converts the frequency to a voltage.

The output converter outputs a voltage or a current corresponding to the displacement of the object, and determines the side of the object relative to a position designated in advance, and outputs the switch output. To be generated.

[0013] Further, the coil used for the displacement detecting section is
By using a copper-nickel-manganese alloy wire (manganin wire) or a copper-nickel alloy wire as the conductive wire, it is possible to further reduce the fluctuation of the output value with respect to a temperature change.

Further, the material of the magnetic body inserted into the inner diameter side of the coil and the pipe-shaped magnetic body inserted into the outer diameter side of the coil of the displacement detecting section is made of 3% silicon iron, amorphous or ferrite. Thus, it is possible to further reduce the fluctuation of the output value with respect to the temperature change.

When the pipe-shaped conductor is moved on the outer diameter side of the coil of the displacement detecting section, a cored coil having a rod-shaped magnetic body as a core is used, so that a small-diameter coil with a smaller number of windings is provided. Can be used.

Further, by making the material of the bar-shaped magnetic material 3% silicon iron, amorphous, or ferrite, it is possible to further reduce the fluctuation of the output value with respect to the temperature change.

Further, in order to compensate for the temperature change of the resistance value of the coil of the displacement detecting section, a thermistor having a negative temperature characteristic is connected in series with the coil, and is arranged in the vicinity of the coil. On the other hand, it is possible to make the fluctuation of the output value smaller.

Further, in order to compensate for the temperature change of the inductance of the coil of the displacement detecting section, a thermistor having a negative temperature characteristic is connected in parallel with the coil, and is arranged near the coil, so that the temperature change can be prevented. Thus, the fluctuation of the output value can be further reduced.

Further, when a rectangular wave having a high level for a fixed time is generated at the rise and fall of the output of the comparator of the oscillation circuit section, the interval between the rectangular waves varies due to a change in the period. By integrating the square wave, it becomes possible to output a change in the oscillation cycle of the output of the comparator as a change in voltage,
The frequency voltage converter can be easily configured.

[0020]

When the power is supplied to the position detector constructed as described above, when no charge is stored in the capacitor, the comparator outputs a high level because the input voltage of the comparator is low. Then, electric charges are stored in the capacitor at a speed determined by the impedance of the coil and the resistor.

Since the pole on the side where electric charge is stored in the capacitor is also connected to the input side of the comparator, the output of the comparator is inverted when a voltage exceeding the threshold value of the comparator is reached after a certain time. Level. The change in the voltage on the input side to the comparator at this time is in the direction of rising from the low voltage, and the determination is made based on the threshold value on the high voltage side.

When the output of the comparator goes low, the charge stored in the capacitor is discharged as soon as it is determined by the impedance of the coil and the resistor.

The discharge causes the voltage on the input side of the comparator to decrease. At this time, the change in the voltage is in the direction of decreasing from the high voltage, and the judgment is made based on the threshold value on the low voltage side. When the input voltage falls below the threshold, the output goes high and charge is stored in the capacitor. Thereafter, by repeating these series of operations, the output of the comparator continues to oscillate.

When electric power is stored in the capacitor when the power is turned on, a low level is output because the input of the comparator is at a high level. Therefore, when the capacitor starts discharging and the voltage becomes low until the voltage exceeds the low-voltage threshold of the comparator, the output of the comparator goes high. Therefore, when the voltage is increased until the capacitor is charged and exceeds the high-side threshold value of the comparator, the output of the comparator becomes low level, and thereafter, a series of these operations are repeated.

As described above, if the power is turned on regardless of the state of the capacitor, the output of the comparator becomes
Start oscillating.

The oscillation cycle is determined by the values of the coil, the resistor and the capacitor. In the position detector, the oscillation cycle of the output of the comparator is changed by changing the impedance of the coil.

In order to change the impedance of the coil, it is necessary to change the inductance of the coil. A method of moving a conductor or a magnetic material at the inner diameter of the air-core coil and a method of moving the conductor or the magnetic material at the outer diameter of the air-core coil are described. A method of moving the pipe-shaped conductor or the magnetic material, and a method of moving the pipe-shaped conductor at the outer diameter portion of the cored coil having the rod-shaped magnetic material as the core can be considered.

In the method of moving the conductor at the inner diameter of the air-core coil and the method of moving the pipe-shaped conductor at the outer diameter of the air-core coil, the magnetic flux generated from the coil causes the eddy current to flow to the surface of the conductor. Is generated, and is converted into heat by the internal resistance of the portion and is lost, so that the magnetic flux passing through the coil is reduced. Therefore, as the conductor is inserted, the inductance of the coil decreases and the impedance also decreases, so that the time for charging and discharging the capacitor is shortened, and as a result, the period of the oscillation of the output of the comparator is shortened.

In the method of moving the magnetic material at the inner diameter of the air-core coil and the method of moving the pipe-shaped magnetic material at the outer diameter of the coil, the magnetic permeability near the coil is reduced at the portion where the magnetic material is inserted. The magnetic flux penetrating the coil increases because of the rise. Thereby, as the magnetic material is inserted, the inductance of the coil increases and the impedance also increases, so that the time for charging and discharging the capacitor is prolonged, and as a result, the oscillation cycle of the output of the comparator is prolonged.

In the method of moving a pipe-shaped conductor at the outer diameter of a cored coil having a rod-shaped magnetic body as a core, the magnetic flux concentrates near the coil because the rod-shaped magnetic body is a core. As a result, the magnetic flux passing through the coil increases, and the inductance of the coil increases as compared with the air-core coil. When a pipe-shaped conductor is inserted in that state, the magnetic flux generated by the coil generates an eddy current on the surface of the conductor,
It is converted to heat and becomes a loss, reducing the magnetic flux passing through the coil, thus reducing the inductance of the coil.
Therefore, since the impedance is also reduced, the time for charging and discharging the capacitor becomes shorter as the pipe-shaped conductor is inserted, and as a result, the period of oscillation of the comparator becomes shorter.

As described above, by changing the inductance and impedance of the coil, the period of oscillation of the output of the comparator is changed, and the position of the object is detected by observing the period.

Further, in order to increase the stability of the position detector with respect to a change in temperature, it is necessary to stabilize the resistance value of the coil which is involved in charging and discharging of the capacitor.
By using a copper-nickel-manganese alloy wire (manganin wire) or a copper-nickel alloy wire having a stable resistance value against a change in temperature for the material of the conductive wire forming the coil, fluctuations in output can be suppressed. .

Further, in order to enhance the stability of the position detector against a change in temperature, it is necessary to stabilize the inductance and impedance of the coil involved in the charging and discharging time of the capacitor. By using 3% silicon iron, amorphous, or ferrite, whose magnetic properties are stable against temperature changes, as the material of the magnetic material inserted into the outer diameter portion, output fluctuation can be suppressed.

Further, in order to enhance the stability of the position detector against a change in temperature, it is necessary to stabilize the inductance and impedance of the coil involved in charging and discharging of the capacitor. By using 3% silicon iron, amorphous, or ferrite, whose magnetic properties are stable with respect to a change in temperature, as the material of the core magnetic material, fluctuations in output can be suppressed.

In order to enhance the stability of the position detector against a change in temperature, there is a method of compensating for a change in the resistance value of the coil portion. A thermistor having a negative temperature characteristic is connected in series with the coil, and the vicinity of the coil is connected. , It is possible to suppress a change in output with respect to a change in temperature of the position detection unit.

In order to enhance the stability of the position detector with respect to a change in temperature, there is a method of compensating for a change in inductance of a coil portion. By arranging, it is possible to suppress a change in output with respect to a change in temperature of the position detection unit.

Further, as a method for easily realizing the function in the frequency-voltage converter of the position detector, a rectangular wave having a high level for a fixed time at the rise and fall of the output of the comparator is provided. Since the interval between the rectangular waves varies due to the change in the cycle, the change in the oscillation cycle of the comparator can be output as a change in the voltage by integrating the rectangular wave.

[0038]

An embodiment will be described with reference to the drawings.
First, the overall configuration will be described. In FIG. 1, a cored coil (3) having a rod-shaped magnetic body (6) as a core
A pipe-shaped conductor (7) that is in contact with, joined to, or integrated with the object to be detected is inserted into the outer diameter side of the pipe.

A coil (3) and a resistor (4) are connected in series between the input side and the output side of an inverted output comparator (2) having a threshold value having hysteresis. Also, connect the capacitor (1) to the input side of the comparator (2),
The other pole of the capacitor (1) is connected to 0V (volt).

Observing the output waveform of the comparator (2),
When a rectangular wave having a high level for a fixed period of time is generated at the rising and falling edges, the density of the rectangular wave is changed due to a change in the period. Therefore, the period of the oscillation of the comparator (2) is integrated by integrating the rectangular wave. change of,
That is, a change in frequency can be output as a change in voltage.

In the output converter, this voltage is output as a voltage or current multiplied by a certain ratio, or a certain position is set in advance, and the object to be detected is located on either side with respect to that position. A position detector is constructed by determining whether or not a switch output is generated.

When a switch output is generated, the voltage obtained by converting the above-mentioned frequency is compared with a voltage level corresponding to the position of the object to be detected for the switch output, and a high level of the switch output is obtained. A configuration that outputs a low level is conceivable.

In the structure of the position detector, particularly by using the method using the cored coil as described above, the coil is wound around the iron core, and the coil is wound in the pressure vessel, so that the fluid pressure can be reduced. For example, as shown in FIG. 5, the piston rod (24) has an outer diameter of 2 mm, and the cylinder tube (25) can be assembled into a cylinder, which has a very simple structure and facilitates miniaturization. 4 mm inside diameter of
It can be easily incorporated into a small pneumatic cylinder with a stroke of 20 mm.

In this embodiment, the position detector (27)
Is fixed to the head cover (26) and inserted into a pipe-shaped metal piston rod (24). When compressed air is injected from the port (28), the piston rod (24) moves forward, When the air is exhausted from the port (28), the piston rod (24) is retracted by the compressed spring (29). In order to detect the position of the piston rod (24) of the small cylinder, a small-sized and simple structure such as the position detector is suitable.

In the configuration diagram shown in FIG. 1, the material of the conductive wire used for the coil (3) is changed with respect to a change in temperature.
By using a copper-nickel-manganese alloy wire (manganin wire) or a copper-nickel alloy wire having a stable resistance value, a change in output due to a change in temperature can be further reduced.

In the configuration diagram shown in FIG. 1, the material of the core made of the magnetic material (6) is made of 3% silicon iron, amorphous, or ferrite whose magnetic properties are stable against temperature changes. Fluctuations in output values due to changes in temperature can be further reduced.

In the configuration shown in FIG. 1, the case for protecting the joint between the coil (3) and the cable is
By connecting a thermistor (9) having a negative temperature characteristic in series with the coil (3) to compensate for the temperature change of the resistance of the coil (3), the fluctuation of the output value due to the temperature change is further reduced. be able to.

In the configuration shown in FIG. 1, the coil (3) is provided in a case for protecting the joint between the coil (3) and the cable in order to compensate the temperature change of the inductance of the coil (3). Thermistor with negative temperature characteristic (1
By connecting 0), it is possible to further reduce the fluctuation of the output value due to a change in temperature.

However, in realizing the small and simple structure which is a feature of the position detector, it is desired to avoid using a thermistor. For this purpose, 3% silicon iron, amorphous, or ferrite is used as the core material of the magnetic body (6), a manganin wire is used for the coil (3), and a pipe-shaped conductor ( 7) is nickel-chromium, iron-chromium, copper-nickel, or copper-nickel-
By using a material whose electric resistance value is stable against a change in temperature such as manganese, an extremely stable output with respect to a change in temperature can be obtained without using a thermistor.

Next, a case where the coil (3) in FIG. 1 is a hollow coil and the conductor (5) or the magnetic body (6) is inserted into the inner diameter of the coil to detect the position will be described.

In this case, it is necessary to make the case for protecting the coil (3) portion of the position detecting section hollow, and it is necessary to determine whether the conductor (5) or the magnetic material (6) moves inside the inner diameter of the coil (3). ) Is fixed on the object to be detected, but the coil (3) uses manganin wire, and the magnetic material (6) inserted into the inner diameter part uses 3% silicon iron, amorphous, or ferrite. Then, thermistors (9) and (10)
An extremely stable output can be obtained even if the temperature is not compensated for by using a temperature change.

In the configuration shown in FIG. 1, the frequency-to-voltage converter (13) is a part that converts the oscillation frequency of the output of the comparator (2) into a voltage. In general, there are many products called frequency-voltage converters, and a method which can be easily realized in this position detector will be described below.

At the rising and falling edges of the output waveform of the oscillating comparator (2), a rectangular wave having a high level for a fixed time is generated. When the oscillation cycle of the comparator (2) changes, the interval between the low-level portions of the rectangular wave changes, so that the frequency can be converted into a voltage by integrating.

Next, temperature compensation using a thermistor will be described. In the configuration diagram shown in FIG. 1, the material of the conductive wire used for the coil (3), the conductors (5) and (7) inserted on the inner diameter side and the outer diameter side of the coil (3), and the magnetic body (6)
If the material of (8) is made of a material having good temperature characteristics as described above, the thermistors (9) and (10) for temperature compensation may not be necessary. When it is difficult to use a material having good temperature characteristics due to factors such as shape, shape, and other factors, it may be easier to perform temperature compensation with a thermistor. Further, by using a thermistor in addition to using a material having good temperature characteristics as described above, the temperature characteristics can be further improved.

The method of temperature compensation using a thermistor will be described as a result of experimentally determining the connection method. A copper wire is used for the coil (3), and iron is used for the magnetic material (6) as the core of the cored coil. When used, the electric resistance of the copper wire changes by about 0.4% / ° C with respect to the temperature change, and the inductance of the cored coil changes by about 0.1 to 0.2% / ° C. The output voltage changes due to the influence.

Therefore, when the temperature of the displacement detection unit (11) is changed in series and in parallel with the coil (3), that is, by attaching a variable resistor instead of the thermistors (9) and (10) in FIG. The resistance value of each variable resistor was found so as to obtain the same output voltage as at the initial temperature. Then, unless both variable resistors were adjusted according to the position of the pipe-shaped conductor (7) inserted on the outer diameter side of the coil, temperature compensation could not be performed over the entire detection range. That is, the pipe-shaped conductor (7)
It was found that the value to be compensated was different depending on the insertion position of.

For this reason, a similar experiment was performed using a manganin wire for the coil (3). Then, without changing the resistance value of the variable resistor connected in series with the coil, the temperature of the entire detection range can be compensated only by changing the resistance value of the variable resistor connected in parallel with the coil. Was completed.

From the above, since the manganin wire has a very stable temperature coefficient of resistance of about 10 PPM / ° C.,
What is compensated by the variable resistor connected in parallel to the coil can be said to be a change in inductance of the cored coil. The value compensated by the variable resistor connected in series to the coil does not need to be adjusted due to the change to the manganin wire, and can be said to be a change in the electric resistance of the coil.

Further, since the resistance value of both variable resistors when the temperature is compensated is such that the resistance value decreases as the temperature rises, a resistor having a negative temperature coefficient of resistance must be used to perform this with a thermistor. It is necessary to change the resistance value in proportion to temperature.In actual use, a fixed resistance and a thermistor are connected in parallel, and the change in the resistance value in a curved line with respect to the temperature of the thermistor is straightened. Need to be done.

[0060]

Since the present invention is configured as described above, it has the following effects.

Since a position detector having excellent temperature characteristics can be constituted by one coil, the structure is very simple, and the oscillation circuit section, the frequency-voltage conversion section and the output conversion section can also be constituted very simply. Therefore, miniaturization is easy as a whole.

In the case of the cored coil system, a sufficient output can be obtained even with a single reciprocating coil, so that the position detecting section is very small and the production is easy. Can be installed.

In a position detector using a coil, a complicated circuit for temperature compensation, which is generally used, or a selection of a constituent material without using a coil for temperature compensation, etc., is used.
Since a stable output is obtained with respect to a change in temperature, the degree of freedom of the coil structure is high, and the coil can be easily mounted on a device.

Further, by simply connecting a thermistor in series with the coil or connecting a thermistor in parallel with the coil and disposing the thermistor in the vicinity of the coil, the stability due to temperature changes can be easily improved. There are many choices, and it is easy to respond to usage environment, size, shape, etc.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a position detector.

FIG. 2 is a configuration diagram of a differential transformer.

FIG. 3 is a graph showing a relationship between a displacement amount of a differential transformer and an output voltage.

FIG. 4 is a cross-sectional view when the differential transformer is incorporated in a hydraulic cylinder.

FIG. 5 is a cross-sectional view when the position detector is incorporated in a small pneumatic cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor 2 Comparator 3 Coil 4 Resistance 5 Conductor 6, 18, 23 Magnetic substance 7 Pipe-shaped conductor 8 Pipe-shaped magnetic substance 9, 10 Thermistor 11 Displacement detection part 12 Oscillation circuit part 13 Frequency voltage conversion part 14 Output conversion Part 15 Excitation coil 16, 17 Detection coil 19 Fluid pressure cylinder 20 Differential transformer 21 Cylinder stroke 22, 24 Piston rod 25 Cylinder tube 26 Head cover 27 Position detector 28 Port 29 Spring

Claims (8)

[Claims] In a position detector for detecting a linear change in position, a capacitor having one pole connected to 0 V (volt) and the other pole connected to an inverted output having a threshold having hysteresis. The output side of the comparator (2) is connected to the input side of the comparator (2) by connecting a coil (3) and a resistor (4) in series to form a circuit connected to the input side of the comparator (2). The output of the comparator (2) is oscillated, and the conductor (5) or the magnetic body (6) is moved on the inner diameter side of the coil (3).
Alternatively, by moving the pipe-shaped conductor (7) or magnetic body (8) on the outer diameter side of the coil (3) to change the inductance of the coil (3), the coil (3) and the resistance (4) are changed. ) Changes, the charging and discharging time of the capacitor (1) changes, and the cycle of oscillation of the output of the comparator (2) changes. By observing the cycle, the coil can be observed. A position detector configured to detect the position of the conductor (5) (7) or the magnetic body (6) (8) moving on the inner diameter side or outer diameter side of (3). 2. A material of a conductive wire forming the coil (3) is selected from a copper-nickel-manganese alloy wire (manganin wire) or a copper
2. The position detector according to claim 1, wherein the position detector is a nickel alloy wire. 3. The material of the magnetic bodies (6) and (8) inserted on the inner diameter side and the outer diameter side of the coil (3) is made of 3% silicon iron whose magnetic properties are stable with respect to temperature changes. 2. The position detector according to claim 1, wherein the position detector is made of amorphous, or ferrite. 4. The position detector according to claim 1, wherein when the pipe-shaped conductor is moved on the outer diameter side of the coil, a cored coil having a magnetic body as a core is used. . 5. The magnetic material (6) according to claim 4, wherein
Position detector made of 3% silicon iron, amorphous, or ferrite. 6. A thermistor (9) having a negative temperature characteristic is connected in series with the coil (3) and arranged near the coil (3) in order to compensate for a temperature change of the resistance value of the coil (3). The position detector according to claim 1, wherein the position detector has a configuration. 7. A thermistor (1) having a negative temperature characteristic to compensate for a temperature change of the inductance of the coil (3).
2. The position detector according to claim 1, wherein the position detector is connected in parallel with the coil, and is disposed near the coil. 8. When a rectangular wave having a high level for a fixed time is generated at the rise and fall of the output of the comparator (2), the interval between the rectangular waves varies due to a change in the period. 2. The position detector according to claim 1, wherein a change in the cycle of oscillation of the output of the comparator is output as a change in voltage by integrating the wave.