JPH0245712A - Position detection device - Google Patents

Abstract

PURPOSE:To make a detection head part small in size by providing two sets of coils obtained by taking two pairs as one set so that their axial lines may be perpendicular to a magnetic substance part and a non-magnetic substance part alternately provided in a moving direction at an equal pitch and making a distance between the central parts of both sets of coils in the moving direction of an object to be detected deviate by 1/4 pitch for the integer multiple of the pitch. CONSTITUTION:The magnetic substance parts 2 and the non-magnetic substance parts 3 are alternately provided at the equal pitches P in the moving direction of a rod 1 on the peripheral surface of the rod 1. The coils 4 to 7 are closely arranged so that their axial lines may be perpendicular to the magnetic substance part 2 and the non-magnetic substance part 3 and arrayed in a line in parallel with the moving direction of the rod 1. Axis-to-axis distances between the respective pairs of coils 4 and 5, 6 and 7 are set as 1/2P and a distance (m) between the central parts of both sets of coils is deviated by 1/4P for the integer multiple of the pitch P. A sine wave voltage + or -asinomegat is inputted in both ends of the coils 4 and 5 and a cosine wave voltage + or -acosomegat is inputted in both ends of the coils 6 and 7, then output voltages V3 and V4 are fetched from the center of the respective pairs of coils.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a position detection device that can detect the position of a detected object with high precision in a non-contact manner.

[Conventional technology]

2. Description of the Related Art Conventionally, there is a position detecting device such as a pneumatic or hydraulic cylinder as shown in FIG. That is, the rod 20, which is the object to be detected, is made of a magnetic material, and strip-shaped non-magnetic material portions 21, such as copper coatings, are provided on the circumferential surface of the rod 20 at equal pitches. Therefore, on the circumferential surface of the rod 20, magnetic portions 22 and non-magnetic portions 21 are provided alternately and at equal pitches in the direction of movement. The detection head section 23 has two
Annular magnetic shielding cores 24 and 25 are provided, and inside one of the shielding cores 24 there are primary coils 26 and 27.
and secondary coils 28 and 29 are arranged so as to surround the rod 20, and a primary coil 30.31 and a secondary coil 32.33 are similarly arranged inside the other shield core 25 so as to surround the rod 20. It is arranged. And the fourth
With respect to the coil group on the left side of the figure, the coil group on the right side is arranged at a position shifted by 1/4 pitch with respect to an integral multiple nP of the pitch P between the magnetic body parts 22 or the non-magnetic body parts 21.

An AC voltage of a cosωt is input to the left primary coil 26.27, and an as
An AC voltage of inωt is input. On the other hand, the voltage induced in the left secondary coil 28, 29 and the right secondary coil 32, 33 changes every pin as the rod 20 moves, and these secondary coils are differentially connected. By doing this, the output voltage of the secondary coil is bsin (ωt
2KX/P).

Here, the principle of operation of the above-mentioned position detection device will be explained in detail, focusing on the coil groups 26 to 29 on the left side of FIG. 4.

FIG. 5 shows that the displacement x of the rod 20 is 0, that is, the non-magnetic part 2
1 is located at the center of the coil group, and in this state the same voltage is induced in the secondary coils 28 and 29, so by differentially connecting both coils 28 and 29, the secondary coils 28 and 29 are The next-side voltage ■1 becomes 0 (V).

FIG. 6 shows a state in which the displacement of the rod 20 is x=P/4, and since the magnetic body part 22 is located in the center of the right coil 27, 29, the induced voltage in the left secondary coil 28 is minimum and the right side The induced voltage in the secondary coil 29 becomes maximum.

FIG. 7 shows a state where the displacement of the rod 20 is x=P/2, and since the magnetic body part 22 is located at the center of the coil group, the fifth
As in the figure, the same voltage is induced in the secondary coils 28 and 29, and the secondary voltage 1 becomes 0 (v).

FIG. 8 shows a state where the displacement of the rod 20 is x-3P/4,
Since the magnetic body portion 22 is located at the center of the left coils 26 and 28, the induced voltage in the left secondary coil 28 is maximum and the induced voltage in the right secondary coil 29 is minimum.

Figure 9 illustrates the primary side voltage (acosωt) and the secondary side voltage ■1 corresponding to the displacement The side voltage V, is in phase with the primary side voltage, and at x=P/2, V+-0, x=
In 3P/4, the phase is opposite to the primary side voltage. In this way, the induced voltage on the secondary side changes as the rod 20 moves, and this is repeated for each pitch. -Next side voltage is rod 2
0 is changed as shown in Figure 9 and induced on the secondary side, so the secondary side voltage ■1 is V, = sin (2πX/P) ・b cosωt
−(1).

Similarly, the secondary voltage ■2 of the coil group 30 to 33 on the right side of Fig. 4 is Vz = cos(2πx/P) ・b sinωt
−” (2).

When these secondary voltages V, , V, are connected differentially as shown in Figure 4, V, −V, = b according to the sine addition theorem.
sin ((11t −2tx/P) ・=(3)
becomes.

Figure 10 shows the input voltage a sin of the primary coil 30.31.
ωt and the output voltage of the secondary coil b sin (ωt−2π
The output voltage is extracted as a signal whose phase is shifted by T (=2πx/P) with respect to the input voltage. Therefore, by measuring this phase shift, it is possible to detect the linear displacement X of the rod 20 within a range of one pitch. Note that if the number of pitches exceeds 1, the linear displacement of the rod 20 can be measured incrementally by counting the number of pitches.

[Problem to be solved by the invention]

Since the above conventional example is a position detection method based on the principle of a differential transformer having a secondary coil and a secondary coil, the coil must necessarily be shaped to surround the rod 2o. Therefore, if the thickness of the rod changes, the diameter of the coil must be changed each time. and,
If the object to be detected is other than a bar-like object such as a rod, for example, if it is a flat member, it cannot be surrounded by a coil, making position detection impossible. In other words, in the conventional example, there are restrictions on the shape of the detected object whose position can be detected.

In addition, since the conventional example requires at least 8 coils,
There is a problem that the number of coils is large and the shape of the detection head section 23 becomes large.

Furthermore, since the output is obtained by reading the secondary coils differentially, it is difficult to correct the sensitivity when there are variations in sensitivity among the coils, making it difficult to obtain high detection accuracy.

Therefore, a first object of the present invention is to provide a position detection device that can use exactly the same coil even if the shape or size of the detected object changes.

A second object is to provide a compact position detection device with a small number of coils.

Furthermore, a third object is to provide a position detection device that can easily correct variations in sensitivity of each coil and has high detection accuracy.

[Structure of the invention]

In order to achieve the above object, the present invention provides an object to be detected in which magnetic parts and non-magnetic parts are provided alternately and at equal pitches in the direction of movement; It is equipped with two sets of two coils arranged close together so that their axes are perpendicular to each other, and the distance m in the direction of movement of the detected object between the central parts of both coil sets is shifted by 1/4 pitch relative to an integer multiple of the above-mentioned pitch. The coils in each set are connected in series,
AC signals having a phase difference of 90'' are input to both ends of each set of coils, and the signals output from the center of each set of coils are differentially detected by an operational amplifier. be.

[Embodiment] FIGS. 1 and 2 show an example in which a position detection device according to the present invention is applied to detecting displacement of a rod 1. In FIG.

On the circumferential surface of the rod 1, magnetic parts 2 and non-magnetic parts 3 are arranged alternately and at equal pitches (
P). Further, the coils 4 to 7 are arranged close to each other so that their axes are perpendicular to the magnetic body part 2 and the nonmagnetic body part 3, and are arranged in a line parallel to the moving direction of the rod 1. Among these coils, coil 4.
5 are connected in series to form one set, and coils 6.7 are also connected in series to form the other set. The distance l between the axes of the coils 4, 5 and 6, 7 in each set is set to z pitch (+AP), and the distance urn between the center parts of the coils 4, 5 and 6, 7 in both sets is set to the above value. It deviates by Subitch with respect to an integral multiple of pitch P. That is, m=nPf/, P (n: integer).

In the examples shown in FIGS. 1 and 2, the settings are as shown in the following equation.

m=P+%P Although FIG. 1 shows the coils 4 to 7 arranged in a line parallel to the moving direction of the rod 1, the present invention is not limited to this. Or they may be arranged spirally, in which case the distance fiffi1m is the rod l
It may be set as the distance in the moving direction.

A cosine wave voltage (±a
cos ωt) is input, a sinusoidal voltage (±a sin ωt) is input to both ends of the coils 6.7 of the other set, and output voltages V, , V4 are taken out from the center of each set of coils.

FIG. 3 shows a specific circuit diagram of the position detecting device. In the drawing, the amplifier circuit 8 includes two phase-inverting amplifiers 9.10.
The input terminal 11 receives a cosine wave voltage signal (
acosωt) is input.

The phase inversion amplifier 9 inverts the phase of the input signal and outputs it to the coil 4.
At the same time, this inverted signal is further inverted by a phase inversion amplifier lO and applied to the other end of the coil 5. Therefore, at both ends of the coil 4.5, there is a cosine wave voltage (±a cos
ωt) is given.

Similarly, the amplifier circuit 12 also includes two phase inverting amplifiers 13.
．． 14, and the input terminal 15 receives a sinusoidal voltage signal (
a sin ωt) is input. Then, after inverting the phases with phase inversion amplifiers 13 and 14, a sinusoidal voltage (±a
sinωt).

Note that the AC voltage signals (a cos ωt, a sin ωt) input to the amplifier circuits 8 and 12 can be easily generated using a known quadrature oscillation circuit.

The magnetic part 2 or the non-magnetic part 3 of the rod l is connected to the coil 4.
5, the inductance of the coils 4 and 5 is equal, so the output voltage V taken out from the center of the coil 4.5 is Ov, and the rod 1 moves to either the magnetic part 2 or the non-magnetic part 2. When the magnetic body portion 3 is shifted from the center of the coil 4.5, the inductances of the coils 4 and 5 on both sides become unbalanced, and a voltage V corresponding to the amount of unbalance is obtained.

Similarly, regarding the coil 6.7, when the magnetic body part 2 or the non-magnetic body part 3 is located at the center of the coil 6.7, the output voltage 4 taken out from the center of the coil 6.7 is O
v, and the magnetic body part 2 or the non-magnetic body part 3 is the coil 6.
If it deviates from the center of 7, a voltage 4 corresponding to the amount of deviation is obtained.

When using unbalanced inductance as in the present invention,
When the input voltage across the coil is a CO3ωL, the waveform obtained at the output is the integral of the input voltage, that is, b sinωt
Conversely, if the input terminals at both ends of the coil are a sin ω, the waveform obtained at the output will be b cos ωt. Since these output waveforms change as shown in FIG. 9 according to the movement of the rod 1, the output voltages V, , V, are expressed by the following equation.

Vx=cos(2+rx/P)・b+sinωt
-(4)Va -5in(2πx/P) ・bz
cosωt −(5) In order to differentially detect the voltages V, , V, an operational amplifier 16 and resistors R+, Rz
, Rs are provided. That is, the voltage V4 is inputted to the negative power of the operational amplifier 16 via the resistor R1, and the output of the operational amplifier 16 is (2). □ is negatively fed back through the resistor R1. Further, a voltage divided by the resistors Rt and Rx of voltage (2) is applied to the positive force. Therefore, the output of the operational amplifier 16 is ■. □ is R1(RI
+R)) R3 As shown in equation (6), the voltage V
, , V4 are multiplied by different coefficients and subtracted from each other for the following reason. That is, since there is inevitably variation in the inductance of each coil 45 and 67, the coefficients b+, bz in equations (4) and (5)
are not necessarily the same. Therefore, simply subtracting the voltage 4 from the voltage 2 does not yield a simple trigonometric function such as equation (3). The above resistance R1Rz, R
If the sO value is adjusted as RI (Rt + R: l) RI, the output will be ■. □ is a simple trigonometric function as shown in the following equation.

Vout = b sin (+u+ t −2πX/
P) This output■. □ is exactly the same as V, -V, in equation (3). Therefore, similarly to FIG. 10, the output voltage ■ with respect to the input voltage a sin ωt. , it is possible to detect the absolute displacement X of the rod 1 within the range of one pitch. It is of course possible to measure the linear displacement of the rod 1 incrementally by counting the number of pitches beyond the pitch (2).

Incidentally, in the above embodiment, the operational amplifier 16 has a voltage of ■.

Although the difference between and (4) is obtained, the same is true even if the sum of these voltages is obtained, and the only difference is whether the phase advances or lags by 2πx/P. Output for sum ■. , becomes as follows.

V. 1It=b sin (ωt+ 2πx/P) In addition, the present invention is not limited to detecting the linear displacement of a round rod, but also detects the linear displacement of a rectangular or flat object to be detected,
Rotational displacement of a disk-shaped object to be detected can also be detected in the same way.

[Effects of the Invention] As is clear from the above description, according to the present invention, changes in coil inductance are detected differentially, so it is only necessary to bring the coil closer to the object to be detected from the outside. There is no need to surround the object to be detected with a coil as in the conventional method. Therefore, even if the shape or size of the object to be detected changes, the same coil can be used, and manufacturing costs can be significantly reduced. Furthermore, the moving direction of the object to be detected is not limited to linear motion, but can also be applied to rotational motion, which greatly expands the range of application.

In addition, since the number of coils used in the present invention is only four,
The number of coils is small, which is economical, and the detection head can be made smaller.

Furthermore, even if there is variation in the sensitivity of each coil, this can be easily corrected by adjusting the gain of the operational amplifier, so extremely accurate position detection is possible.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of an example in which the position detection device according to the present invention is used to detect displacement of a rod, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, Fig. 3 is its circuit diagram, and Fig. 4 is the structural diagram of the conventional example,
5 to 8 are enlarged sectional views showing the operation, FIG. 9 is a waveform diagram of the primary side voltage and secondary side voltage, and FIG. 10 is a waveform diagram of the input voltage and output voltage. DESCRIPTION OF SYMBOLS 1... Rod (detected object), 2... Magnetic material part, 3... Non-magnetic material part, 4-7... Coil, 16... Operational amplifier.

Claims (1)

[Claims] (1) A detected object in which magnetic parts and non-magnetic parts are provided alternately and at equal pitches in the direction of movement, and the object is placed close to the magnetic part and non-magnetic part so that the axis is perpendicular to the magnetic part and the non-magnetic part. The distance m in the moving direction of the object to be detected between the central parts of both coil sets is shifted by 1/4 pitch relative to an integral multiple of the above-mentioned pitch, and the coils of each set are are connected in series with each other, AC signals with a phase difference of 90° are input to both ends of each set of coils, and the signals output from the center of each set of coils are differentially detected by an operational amplifier. A position detection device characterized by: