JPH03214003A - Non-contact displacement sensor - Google Patents

Abstract

PURPOSE:To improve the resistance against electromagnetic noise and to improve detecting accuracy by improving frequency characteristics by providing a detecting coil and an inductance detecting means. CONSTITUTION:A detecting coil 1 is formed by forming a winding 3 around a core 2 wherein thin plates of iron-based amorphous alloy whose high-frequency loss is small are laminated. Both ends of the core 2 are made to face an object 4 and arranged at a fixed state. An oscillator 5, an detector 6 and a filter 7 constitute a inductance detecting means. In this constitution, when an AC at a high frequency is supplied to the winding 3 from the oscillator 5, the increase in magnetoresistance of the core 2 in the closed magnetic path constituted of the detecting coil 1 is suppressed. Therefore, magnetoresistance component caused with a gap epsilon becomes large, and the inductance change due to the displacement of the object 4 becomes large. Thus sensitivity is improved. When the oscillating frequency of the oscillator 5 is set in the flat region of the inductance, the inductance with respect to the modulated wave caused by the displacement of the object 4 becomes approximately constant, and the measuring accuracy is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a non-contact displacement sensor that detects the displacement of an object in a non-contact state, and particularly to an inductance change detection type displacement sensor.

(Prior Art) In recent years, magnetic bearings have been proposed that use magnetic attraction to support a rotating shaft in a non-contact manner, and are attracting attention for their potential for ultra-high speed rotation. This magnetic bearing uses a non-contact displacement sensor that detects the displacement of an object in a non-contact state. Control based on displacement (2) realizes non-contact support of the rotating shaft.

As non-contact displacement sensors used in such magnetic bearings, inductance change detection type displacement sensors are widely known because they have features such as a wide measurement range and large output. This inductance change detection type displacement sensor uses the object as a part of the closed magnetic path of a coil with an iron core2.When the air gap between the coil and the object changes due to the displacement of the object, the magnetic resistance of the closed magnetic path increases. As the inductance of the coil changes, this change in inductance is detected by supplying an alternating current of a predetermined frequency to the coil and measuring the voltage across the coil to detect the displacement of the object. .

(Problems to be Solved by the Invention) In the conventional inductance change detection non-contact displacement sensor as described above, when considering the above-mentioned response to the ultra-high speed rotation of the magnetic bearing, it is necessary to , it is necessary to shorten the rotor length of the magnetic bearing to improve the bending resonance point of the rotating shaft, which reduces the distance between the motor and bearing electromagnet and the displacement sensor. Since the windage loss of the rotating shaft increases with the rise of the displacement sensor, a high-output motor is required, and as a result, electromagnetic noise to the displacement sensor increases significantly, and countermeasures are required.

Further, in conventional non-contact displacement sensors, the core of the detection coil is usually made of a silicon steel plate, and has a characteristic that the inductance decreases as the frequency increases, as shown in FIG. Therefore, the inductance changes due to a change in the frequency of the input signal due to a change in the power supply voltage or a modulated wave caused by the displacement of the object, resulting in a decrease in detection accuracy.

Therefore, the present invention aims to improve the resistance to electromagnetic noise and frequency characteristics of a non-contact displacement sensor that detects changes in inductance, thereby improving detection accuracy.

(Means for Solving the Problems) In order to solve the above problems, the present invention has a core made of an amorphous alloy with low high frequency loss, and is installed opposite to an object to partially cover the object. and an inductance detection means for applying a signal of a predetermined frequency to the detection coil to detect the inductance of the detection coil, and the use of the inductance detection means. The signal is set in a frequency range in which the inductance change characteristic with respect to the frequency of the detection coil is flat.

(Operation and Effects of the Invention) In the present invention configured as described above, the signal supplied from the inductance detection means to the detection coil needs to be set very high with respect to the frequency of displacement of the object. By constructing the core of the detection coil using an amorphous alloy with a small The sensitivity of the sensor is improved, and the influence of the electromagnetic nozzle as a disturbance can be reduced. In addition, the frequency versus inductance characteristic of a detection coil whose core is made of an amorphous alloy has a region where the inductance does not change with respect to frequency changes, so the frequency of the signal supplied to the detection coil should be set near the center of this frequency region. Therefore, even if a modulated wave or the like is generated due to the displacement of the object, the inductance does not change, the frequency characteristics of the sensor become flat, and the detection accuracy improves.

(Example) FIG. 1 is a diagram showing an example of the present invention. In Fig. 1, a detection coil 1 is a roughly U-shaped core 2 made of laminated thin plates of iron-based amorphous alloy with low high-frequency loss, and a winding 3 wound around the outer circumference of the core 2, which detects displacement. The core 2 is fixedly placed on the object 4 with both ends facing each other. 5, 6, and 7 are an oscillator, a detector, and a filter, respectively, constituting the inductance detection means. The AC output of the oscillator 5 is supplied to one end of the winding M3 of the detection coil l. The other end of the winding 3 is grounded to measure the voltage across the winding 3, and one end to which the AC input is supplied is connected to a detector 6. terminal voltage is detected. The output of the detector 6 is supplied to a low-pass or notch filter 7, or a filter 7 that is a combination of both, and only the displacement component of the object 4 is extracted.

Here, the output impedance of the oscillator 5 is larger than the input impedance of the winding 3, and the AC output from the oscillator 5 is a constant current output. In addition, object 4 is at least core 2
The detection coil 1 forms a closed magnetic path passing through the core 2, the gap ε between the core 2, the object 4, and the object 4. In this closed magnetic path, the magnetic resistance of the air gap ε is larger than that of the core 2 and the object 4 made of magnetic material, and when the air gap ε changes due to the displacement of the object 4, the magnetic resistance in the closed magnetic path changes greatly, and the detection The inductance of coil 1 changes. This inductance change is detected by applying a constant AC current to the winding 3 using the oscillator 5 as described above, detecting the voltage across the winding 3 using the detector 6, and smoothing the AC voltage using the filter 7 to generate a displacement component of the object 4. Detect only.

At this time, the oscillation frequency of the oscillator 5 needs to be set to a sufficiently higher frequency than the frequency of the displacement of the object 4 to be detected. On the other hand, when using the detection coil 1 having the core 2 made of an iron-based amorphous alloy, there is a flat inductance region in the high frequency region where the inductance does not change and remains almost constant as the frequency changes, as shown in FIG. Its existence has been confirmed by experiment. Therefore, in this embodiment, the oscillation frequency of the oscillator 5 is set near the center of this inductance flat region.

In the above configuration, since the core 2 is made of an amorphous alloy with low high frequency loss, when a high frequency alternating current is supplied from the oscillator 5 to the winding 3, the magnetic field in the closed magnetic circuit formed by the detection coil 1 is reduced. Since the increase in the magnetic resistance of the body part (i.e., the core 2) is significantly suppressed, the magnetic resistance component due to the air gap ε between the core 2 and the object 4 in the total magnetic resistance of the closed magnetic path is large, and the object The change in inductance due to the displacement of 4 becomes large, and the sensitivity of the sensor improves. In addition, by setting the oscillation frequency of the oscillator 5 in the inductance flat region, which is a frequency characteristic unique to the core 2 made of amorphous alloy, which did not exist in the frequency characteristic of the conventional silicon steel plate core (see Figure 3), the target The inductance is almost constant even with respect to modulated waves due to the displacement of the object 4, and the frequency characteristics as a sensor are good, and detection accuracy is improved. In this way, according to this embodiment, the sensitivity of the non-contact displacement sensor can be improved, and the frequency characteristics can be flattened to improve detection accuracy, so it is resistant to disturbances such as electromagnetic noise, and the ultra-high rotation speed of the magnetic bearing can be improved. It is also possible to respond to

Note that the sensitivity of the sensor can be further improved by using an amorphous alloy for the portion of the object whose displacement is to be detected, in which the closed magnetic path formed by the detection coil is formed. In addition, although the configuration in the above embodiment was such that the displacement of the target object was detected using a single detection coil, a displacement sensor having a configuration in which two or more known detection coils are connected in a bridge manner (one may be a dummy) may also be used. The invention has similar effects. Further, in the embodiment described above, a constant AC current is passed through the detection coil to detect the voltage across the coil, but the detection coil may be driven with a constant AC voltage to detect the current flowing through the detection coil. Further, the filter 7 is not necessarily required for control.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing frequency versus inductance characteristics of an embodiment of the present invention.
FIG. 3 is a diagram showing frequency versus inductance characteristics of a conventional non-contact displacement sensor. 1...Detection coil, 2...Core, 3...Winding, 4...Target, 5 ......Oscillator, 6......Detector, ......Filter.

Claims (2)

[Claims] (1) A detection coil that has a core made of an amorphous alloy and is placed facing an object to form a closed magnetic path that includes a part of the object, and a signal of a predetermined frequency is applied to the detection coil. A non-contact displacement sensor comprising: an inductance detection means for detecting inductance of the detection coil. (2) The inductance detection means sets the frequency of the signal applied to the detection coil to a frequency range in which the inductance change characteristic with respect to the frequency of the coil is flat. Contact displacement sensor.