JPH0743105A - Position transducer - Google Patents

Abstract

PURPOSE:To eliminate an influence on a detector due to a change in temperature by connecting a plurality of coils in series for keeping the sum of coil impedance constant even upon the motion of a magnetic substance, and measuring an impedance change on the basis of the output voltage of the coils. CONSTITUTION:When a core 3 is positioned at the center of a plurality of coils S1 and S2, the impedance values Z1 and Z2 thereof are equal to each other, and coil output voltage becomes a half of exciting voltage. When the core 3 or a spool 8 moves in a negative X (left) direction, the impedance value Z1 becomes larger than the value Z2, and voltage applied to the coil S1 becomes larger than voltage applied to the coil S2, thereby reducing the coil output voltage. Thus, the coil output voltage proportional to the travel distance of the core 3 can be provided. Also, both coils have the same temperature characteristics, and even when temperature changes, the coil output voltage does not change, regardless of the change of the impedance values Z1 and Z2 by the same ratio. Thus, the output of a detector where the coil output voltage is entered, becomes independent of ambient temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device, for example, a position detecting device for detecting the position of a spool in a valve which controls a hydraulic pressure by moving a spool of a hydraulic device, and a precision device which requires precise position detection. It can be used for a position detection device and the like.

[0002]

2. Description of the Related Art Generally, there is a differential transformer type position sensor in a position detecting device. The differential transformer type position sensor uses electromagnetic induction, and is composed of a primary coil P and secondary coils S1 and S2 as shown in FIGS. FIG. 4 shows a sensor portion of this differential transformer type position detecting device, in which a coil bobbin 9 is wound with an input coil P and output coils S1 and S2, and at the center of the coil bobbin 9, a core connected to an object to be measured. 3 is installed so as to be movable in the X direction. A circuit diagram of this differential transformer type position detecting device is shown in FIG. 5, and its operation will be described below. Figure 5
Of the position detecting device is a constant AC voltage input E to the primary coil P.
induced electromotive force E generated in the secondary coils S1 and S2 by adding p
The configuration is such that the difference voltage Es between s1 and Es2 is taken out as a secondary voltage output. And specifically, the core 3 of the magnetic material is +
When it moves in the X direction, the induced electromotive force Es1 becomes the induced electromotive force Es.
Since it becomes larger than 2, the output voltage Es increases. on the other hand,
When the magnetic core 3 moves in the −X direction, the induced electromotive force E
Since s1 is smaller than the induced electromotive force Es2, the output voltage E
s becomes small. Thus, the output voltage Es is proportional to the moving direction of the core 3 and the relative positional relationship between the coil and the core. The applied AC voltage has an excitation frequency of about 200 to 5000 Hz in order to obtain sensitivity and responsiveness.

[0003]

In the above conventional position detecting device for a differential transformer, it is difficult to compensate for an error caused by a temperature difference even if the voltage on the primary side is constant, and the temperature compensating circuit is complicated. However, there is a problem that the circuit becomes expensive and the cost increases. In addition, it is necessary to increase the efficiency of electromagnetic induction, and in order to increase the efficiency of the magnetic circuit, a structure that does not leak magnetic is required, so there is a problem that the shape of the coil cannot be arbitrarily selected, and in order to increase the efficiency of electromagnetic induction. To
There is a problem that it is necessary to increase the number of turns of the coil, the weight of the coil becomes large, and it takes time to manufacture, and these problems also lead to cost increase and are not suitable for mass production. I had it.

[0004]

In order to solve the above problems, the present invention does not measure the output by electromagnetic induction but measures the impedance ratio of the coil and the voltage applied to the coil. To detect. With this configuration, the design and configuration of the coil can be simplified and the cost can be suppressed. For example, two coils are connected in series, a magnetic body is arranged at the center thereof, and the structure is such that the sum of the impedances of the two coils is kept constant even if the magnetic body moves. Also,
The coil may be moved. Then, the coils connected in series are excited with an AC voltage, the output voltage of the coil is measured, and the impedance thereof is indirectly measured. The output voltage of the coil is passed through a detection circuit to obtain an output.

[0005]

The coil excited by the AC voltage has a coil inductance in addition to the resistance corresponding to the coil winding. When the two coils are installed so that the total impedance of the two coils is kept constant even if the core moves, the inductance of these coils changes due to the change of the magnetic permeability due to the change of the position of the core. . Therefore, the impedance of the coil changes depending on the position change of the core. That is, the position of the core of a magnetic material having a high magnetic permeability changes in the coil. Therefore, when an AC voltage is applied to the entire coil, the potential at the connection point of the two coils is equal to the impedance of the coil caused by the position change of the core. It changes according to changes. By measuring this potential, the position change of the measurement object can be read.

The impedance of the two coils is Z
1, Z2 and the voltage across the coil is E,
The output voltage V at the connection point of the two coils (hereinafter referred to as the output voltage of the coil) is V = E · Z1 / (Z1 + Z2) (1) Therefore, the output voltage V of the coil is the ratio of the impedances of the two coils. By the way, since these two coils have the same temperature characteristics, the output voltage V of the coils is constant even if the impedances Z1 and Z2 of the two coils change by the same ratio. Therefore, the output voltage of the coil remains constant even if the temperature changes. The output voltage of this coil is input to the detection circuit. Therefore, the output of the detection circuit does not affect the change in temperature.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the position detecting device of the present invention will be described with reference to FIGS. The present embodiment is an example using two coils.

FIG. 1 is a sectional view of an embodiment of the sensor portion of the position detecting device of the present invention, which is a stroke sensor for detecting the position of the spool of a hydraulic device. Reference numeral 1 is a sensor unit of the position detecting device, that is, a stroke sensor, 2 is a coil wound around a coil bobbin 9, and 3 is a core made of a magnetic material, which is connected to a spool 8 via a shaft 4 and It is designed to detect movement. Further, the oscillation circuit and the detection circuit for exciting the coil are installed inside the case 6 as the built-in circuit 5. By the way, in this embodiment,
Although the core made of a magnetic material is arranged in the center of the coil, the magnetic material may be arranged outside the coil.

FIG. 2 is a block diagram of the position detecting device of the present invention. The output transmitted by the transmission circuit 10 is input to the terminal 1 of the coil 2, and the output voltage V of the coil is generated at the terminal 2. This voltage is input to the detection circuit 11, and the detection circuit 11 adjusts the amplitude and average value of the output voltage V, that is, the gain and offset so that the output of the detection circuit has a desired output characteristic. These transmission circuit 10 and detection circuit 1
1 and the built-in circuit 5 are configured, and the output of the detection circuit 11 is connected to, for example, a position display device or a position control circuit (not shown).

The operation of the position detecting device of the present invention will be described with reference to FIG. With the excitation voltage applied,
When the core 3 is located at the center of the two coils S1 and S2 as shown in b, the impedance of the two coils is Z1 = Z
2, the output voltage of the coil is exactly 1/2 of the excitation voltage.
become. When the core 3 moves in the −X direction as shown in FIG. 3a, the impedances Z1 and Z of the two coils S1 and S2 are
2 becomes Z1> Z2, and the voltage applied to S1 becomes larger than the voltage applied to S2.
It will be smaller than when. Conversely, when the core 3 moves in the + X direction, the impedances Z1 and Z2 of the two coils are
Becomes Z1 <Z2 and the voltage applied to S2 becomes larger than the voltage applied to S1. Therefore, the output voltage of the coil is as shown in FIG.
It will be bigger than when. In this way, when the core moves, it is possible to obtain an output voltage of the coil that is proportional to the moving amount. Furthermore, since the two coils have the same temperature characteristics even if the temperature changes, the output voltage of the coil does not change even if Z1 and Z2 change by the same ratio according to the equation (1). The output of the input detection circuit also becomes a stable output regardless of the ambient temperature.

FIG. 6 shows a modification of the coil winding method. FIG. 6a is an example in which the number of turns of the coil 1 is larger than that of the coil 2, and FIG. 6b is an example in which the two coils 1 and 2 are wound in a superposed manner. As described above, the winding method of the coil is not limited to the embodiment, and the winding method of the coil is a design matter, and various winding methods can be considered. In the winding method of FIG. 6a, since the number of windings of the coil 2 is smaller than the number of windings of the coil 1, the sensitivity to the movement of the core in the −X direction is higher than the sensitivity to the movement of the core in the + X direction in the X-axis direction. Becomes higher. Further, the winding method shown in FIG. 6B has a feature that the coil is compact.

[0012]

Since the position detecting device according to the present invention detects a position by detecting a change in impedance, the number of turns of the coil can be remarkably reduced as compared with the conventional differential transformer type. The cost can be reduced, and the magnetic circuit can be made compact.

Further, since the output voltage is proportional to the ratio of the impedances of the plurality of coils, the output voltage becomes constant even if the impedance changes due to temperature, which has a remarkable effect that a stable output can be obtained. .

[Brief description of drawings]

FIG. 1 is a sensor section of a position detecting device according to the present invention.

FIG. 2 is a block diagram of a position detecting device according to the present invention.

FIG. 3 is an operation explanatory diagram of a sensor unit of the position detection device of the present invention.

FIG. 4 is a sensor section of a conventional position detection device.

FIG. 5 is a circuit diagram of a conventional position detection device.

FIG. 6 is a modified embodiment of the sensor coil of the position detecting device of the present invention.

[Explanation of symbols]

1 ... Stroke sensor, 2 ... Coil, 3 ... Core, 4 ... Shaft, 5 ... Built-in circuit, 6 ... Case, 7 ... Mold resin, 8 ... Spool, 9 ... Coil bobbin, 10 ... Oscillation circuit, 11 ... Detection circuit, P ... input coil, S1, S2 ... output coil.

Claims (1)

[Claims] 1. A plurality of coils connected in series that are excited by an alternating current, and a core made of a magnetic material that is movably inserted in the coils. In a position detection device that detects the position of a measurement object connected to a core, arrange multiple coils and cores so that the total impedance of the coils is constant even if the core moves, and change the relative position of the coils. A position detecting device for detecting the position of a measuring object by detecting the impedance change due to the output voltage of the coil.