JP2003148904A - Eddy current type displacement sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current type displacement sensor for magnetic bearing suitable as a displacement sensor for detecting the displacement of an object to be supported by a magnetic levitation device used under an extremely low temperature. SOLUTION: This displacement sensor is provided with a displacement sensor winding 3 and a sensor target 2 opposed to the displacement sensor winding 3, and detects the displacement of an object to be supported by the magnetic levitation support device for magnetically levitating and supporting the object to be supported under an extremely low temperature. The displacement sensor winding 3 is wound on and fixed to a magnetic pole 4 consisting of a laminated type magnetic material or a magnetic material hardly generating an eddy current. The sensor target 2 opposed to the displacement sensor winding 3 is the object to be supported (rotating shaft 8) or a sleeve fixed to the object to be supported, and the frequency of a carrying signal to be supplied to the displacement sensor winding 3 is set to several tens KHz or more and MHz order or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing or the like for magnetically levitating and supporting a support object such as a rotating shaft of a machine used at ultra-low temperature such as a pump for transferring ultra-low-temperature liquefied gas such as liquid hydrogen and liquid helium. The present invention relates to an eddy current displacement sensor for detecting a displacement of a support target used in the magnetic levitation support device.

[0002]

2. Description of the Related Art In a pump or the like for transferring an extremely low temperature liquefied gas such as liquid hydrogen or liquid helium, high speed rotation may be required because the liquid quality is low. Oil bearings that freeze and solidify cannot be used as bearings for rotary machines that are used under such extremely low temperatures. Ball bearings, hydrostatic bearings, and magnetic bearings are available as bearings. Each bearing has advantages and disadvantages, ball bearings are relatively available, but continuous high-speed rotation is not reliable in terms of lubrication, and hydrostatic bearings have a concern about support rigidity because the liquid is diluted. Since it does not work at low speed, there is concern about wear.

On the other hand, although the magnetic bearing is expensive, it can be expected to have the same performance as a magnetic bearing used at room temperature even at an extremely low temperature, and can be used from low speed to high speed rotation. As a displacement sensor that detects the displacement of the shaft used in magnetic bearings, a so-called induction type displacement sensor that positively configures a magnetic circuit through a gap and detects the change in inductance due to the change in the gap with a coil The principle is different from this, but the gap is the same, but the magnetic circuit is not actively constructed, and the change in the gap changes the intensity of the eddy current generated by self-induction action, which is commonly known as detecting the impedance change of the coil. There are eddy current displacement sensors.

FIG. 1 is a diagram showing the structure of a conventional inductive displacement sensor. FIG. 1 (a) shows a plan structure and FIG. 1 (b) shows a side structure. In FIG. 1, reference numeral 10 denotes a target side structure of the inductive displacement sensor. As shown in the figure, the target side 10 has a sensor target 13 in which steel sheets with a magnetic material having an insulating coating are laminated on a rotary shaft 11 made of, for example, a magnetic material via a sleeve 12 made of a non-magnetic material. A sensor winding 14 is attached to a magnetic pole 15 made of a laminated magnetic material so as to face the sensor target 13.

In the inductive displacement sensor having the above structure, when exposed to a large temperature change from room temperature to extremely low temperature such as liquid hydrogen and liquid helium, the sensor target 13 made of a magnetic material is separated from the rotary shaft 11 made of a magnetic material. Since thermal stress is generated between the non-magnetic material sleeves 12 interposed therebetween, attention must be paid when designing and manufacturing the same. In addition, since the sensor target 13 is a magnetic material, there is a considerable restriction on the magnetic material that can be used in consideration of its strength in order to avoid brittle fracture at extremely low temperatures. Therefore, a displacement sensor that does not require a special configuration as the sensor target 13 is desired.

2A and 2B are views showing a configuration example of a conventional eddy current type displacement sensor. FIG. 2A shows a plan configuration and FIG. 2B shows a side configuration. In FIG. 2, the sensor winding 16 is arranged so as to face the rotating shaft 11. The sensor winding 16 is basically an air-core coil, and is protected by a resin or ceramic protective layer 17, and the protective layer 17 is bonded to a metal protective portion 18.

In the eddy current displacement sensor having the above structure, the rotary shaft 11 can be used as it is as a sensor target for the inductive displacement sensor. Further, the sensor target may be not only a magnetic material but also a non-magnetic conductor, which is advantageous in terms of brittleness. However, as described above, the sensor winding 16 of the usual eddy current displacement sensor is an air core coil. This is because if the sensor winding 16 has a metal core, eddy current is also generated in this metal core, and only the effect of the eddy current originally generated in the sensor target material cannot be detected. Therefore, in the usual eddy current displacement sensor, the sensor winding 16 is an air-core coil, and the air-core coil is protected by a resin material or a ceramic material.

However, when the resin material is protected at extremely low temperatures such as liquid hydrogen and liquid helium, the fixing of the air-core coil may be jeopardized due to the cracking of the resin material. In the case of ceramic protection, it takes a lot of time to fire the ceramic, there is a fear of cracking like a resin material at an extremely low temperature, or it is difficult to join the metal protection part 18, and it is very expensive to cope with these. There is a problem that it becomes a sensor.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is used as a displacement sensor for detecting the displacement of a supporting object for a magnetic levitation supporting device, which is used at extremely low temperatures. An object of the present invention is to provide a suitable eddy current displacement sensor for a magnetic bearing.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a displacement sensor winding and a sensor target facing the displacement sensor winding, and the object to be supported at an extremely low temperature. Is an eddy current type displacement sensor for detecting a displacement of an object to be supported of a magnetic levitation supporting device for magnetically levitation, wherein the displacement sensor winding is wound around a laminated magnetic material or a magnetic material in which eddy current is hard to occur and fixed. , The sensor target facing the displacement sensor winding is a supporting object or a sleeve fixed to the supporting object, and the frequency of the carrier signal supplied to the displacement sensor winding is several tens of kilohertz or more and megahertz or less. Is characterized by.

In the eddy current type displacement sensor, when the displacement sensor winding is wound and fixed on the magnetic material as described above, the effect of mechanically fixing is great, but the eddy current generated there is preferable for the eddy current type displacement sensor. is not. Therefore, since the displacement sensor winding is wound around and fixed to the laminated magnetic material or the magnetic material in which the eddy current does not easily occur, the generation of the eddy current which is not preferable for the eddy current displacement sensor is suppressed. Further, since the temperature is extremely low, the electric resistance of the support target serving as the sensor target or the sleeve fixed to the support target becomes small, which is preferable for generating the eddy current. Further, by setting the frequency of the carrier signal to several tens of kilohertz or more to the megahertz order or less, the magnetic flux generated in the laminated magnetic material that is the metal core of the displacement sensor winding or the magnetic material in which eddy current is hard to occur includes the sensor target. However, a magnetic path is formed, though not a magnetically closed circuit, which is a preferable result for the eddy current displacement sensor.

According to a second aspect of the present invention, in the eddy current type displacement sensor according to the first aspect, the displacement sensor winding is covered with a mechanical protective material, and is fixed by impregnating a resin. .

As described above, by covering the displacement sensor winding with the mechanical protection material and fixing it by impregnating it with a resin, it is possible to withstand a large temperature from normal temperature to extremely low temperature.

The invention according to claim 3 is the invention according to claim 1 or 2.
The eddy current type displacement sensor described in (1) above is characterized in that an insulating layer is interposed between the mechanical protection member and the displacement sensor winding.

As described above, since the insulating layer is interposed between the mechanical protective material and the displacement sensor winding, when a metal material is used as the mechanical protective material, a large temperature from normal temperature to ultra-low temperature is obtained. It is possible to withstand the thermal stress due to the change and improve the insulating property.

The invention according to claim 4 is the invention according to claims 1 to 3.
In the eddy current type displacement sensor described in (1), the magnetic levitation support device is a magnetic bearing that levitationally supports a rotation shaft that is an object to be supported.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a diagram showing a schematic configuration of an eddy current displacement sensor for a magnetic bearing according to the present invention.
FIG. 3A shows a plan configuration, and FIG. 3B shows a side configuration. FIG. 4 is a diagram showing a configuration example of the displacement sensor block on the displacement sensor side. Reference numeral 1 denotes a displacement sensor block on the displacement sensor coil side of the eddy current displacement sensor, and 2 denotes a sensor target. Displacement sensor winding 3 of the displacement sensor block 1
Is wound around a magnetic pole 4 made of a laminated magnetic material or a magnetic material in which eddy current is hard to generate so that it does not fall off even when exposed to ultra-low temperature liquefied gas. The protective material 6 is fixed and impregnated with the resin material 7 to be fixed. A metal material is used for the mechanical protection material 6, and an epoxy resin material is used as the resin material 7.

The sensor target 2 facing the displacement sensor constituted by the displacement sensor winding 3 and the magnetic pole 4 made of a laminated magnetic material is a rotating shaft 8 having conductivity or magnetism. The sensor target 2 and the rotating shaft 8 are preferable as an eddy current type displacement sensor because their electrical resistance is lowered at an extremely low temperature and an eddy current easily flows. As the sensor target 2, a sleeve made of a material having conductivity or magnetism fixed to the rotating shaft 8 may be used.

The winding of the displacement sensor winding 3 around the magnetic pole 4 made of a laminated magnetic material or a magnetic material in which eddy current is hard to occur is usually performed by an inductive sensor, but here, a glass cloth or the like is used. Fixing is performed by a mechanical protective material (metal material) 6 through the folded insulating layer 5 and the like, and the resin material 7 is impregnated and fixed. The presence of the metal core of the displacement sensor winding 3 has a great effect of mechanically fixing the displacement sensor winding 3, but the eddy current generated there is not preferable for the eddy current displacement sensor. Therefore, here, since the laminated magnetic material or the magnetic material in which the eddy current is hard to occur is used for the magnetic pole 4 around which the displacement sensor winding 3 is wound, the generation of the eddy current can be suppressed.

When the frequency of the carrier signal flowing through the displacement sensor winding 3 is on the order of mega Hz or more as in the case of an ordinary eddy current type sensor, the effect of the eddy current generated in the magnetic pole 4 serving as the metal core of the displacement sensor winding 3 is exerted. Is large, which is not preferable as an eddy current sensor. Therefore, here, the generation of the eddy current is suppressed by using the laminated magnetic material or the magnetic material in which the eddy current is hard to be generated in the magnetic pole 4 as described above.

Further, the frequency of the carrier signal supplied to the displacement sensor winding 3 is shifted to a relatively low frequency range from several tens of kilohertz to less than mega-Hz order. In the eddy current type displacement sensor of this embodiment, this is not a closed magnetic circuit, but the displacement sensor winding 3 is wound around the magnetic pole 4 made of a laminated magnetic material or a magnetic material in which eddy current is hard to occur. This is because it is considered that a magnetic circuit that tries to intersect magnetic flux is formed in the sensor target 2 and that the frequency characteristic is lower than the mega Hz order due to the influence of the magnetic characteristic of the magnetic material.

The present invention utilizes the sensor winding magnetic pole of the inductive displacement sensor and the sensor target of the eddy current displacement sensor, which usually have different principles, but in order to match them together, the displacement sensor winding is used. It utilizes the idea of lowering the frequency of the carrier signal supplied to the wire and the phenomenon of low electrical resistance of the sensor target material at extremely low temperatures.

In the above embodiment, the displacement sensor for detecting the displacement of the rotating shaft in the magnetic bearing that magnetically levitates and supports the rotating shaft has been described as an example. However, the application field of the eddy current displacement sensor according to the present invention is not limited to this. It is not limited to this,
It can be widely used for an eddy current type displacement sensor for detecting the displacement of a support target of a magnetic levitation support device used at extremely low temperatures such as liquid hydrogen and liquid helium.

[0024]

As described above, according to the invention described in each claim, the displacement sensor winding is wound and fixed on the laminated magnetic material or the magnetic material in which the eddy current is hard to occur, and the displacement sensor winding is Since the opposing sensor target is a supporting object or a sleeve fixed to the supporting object, and the frequency of the carrier signal supplied to the displacement sensor winding is set to several tens of kilohertz to megahertz or less, the following excellent The effect is obtained.

(1) Even when exposed to an atmosphere whose temperature changes from room temperature to ultra-low temperature such as liquid hydrogen and liquid helium,
No special configuration is required for the sensor target.

(2) Compared with the air core coil of a normal eddy current type displacement sensor, the displacement sensor winding is wound around a laminated magnetic material or a magnetic material in which an eddy current is less likely to occur, so that the displacement is generated even at an extremely low temperature. It is possible to hold the sensor winding. Further, there is no need to protect with an expensive ceramic, and there is no difficulty in joining the ceramic or resin and the metal case. Therefore, the eddy current displacement sensor can be provided at a relatively low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a conventional inductive displacement sensor, FIG. 1 (a) is a plan configuration, and FIG. 1 (b) is a side configuration.

FIG. 2 is a diagram showing a configuration example of a conventional eddy current displacement sensor, FIG. 2 (a) is a plan configuration, and FIG. 2 (b) is a side configuration.

3A and 3B are diagrams showing a schematic configuration of an eddy current displacement sensor according to the present invention, wherein FIG. 3A is a plan configuration and FIG. 3B is a side configuration.

FIG. 4 is a diagram showing a configuration example of a displacement sensor block of an eddy current displacement sensor according to the present invention.

[Explanation of symbols]

1 Displacement sensor block 2 sensor targets 3 Displacement sensor winding 4 magnetic poles 5 insulating layers 6 Mechanical protection material 7 Resin material 8 rotation axes

Claims (4)

[Claims] 1. A displacement detection coil of a magnetic levitation support device, which comprises a displacement sensor winding and a sensor target facing the displacement sensor winding, and magnetically supports a support target under ultra-low temperature, to detect the displacement of the support target. An eddy current type displacement sensor, wherein the displacement sensor winding is wound around and fixed to a laminated magnetic material or a magnetic material in which eddy current is unlikely to occur, and the sensor target facing the displacement sensor winding is the support target or the An eddy current type displacement sensor, characterized in that a sleeve fixed to an object to be supported is used, and a frequency of a carrier signal supplied to the displacement sensor winding is set to several tens of kilohertz to megahertz. 2. The eddy current displacement sensor according to claim 1, wherein the displacement sensor winding is covered with a mechanical protective material and is fixed by being impregnated with resin. 3. The eddy current displacement sensor according to claim 1, wherein an insulating layer is interposed between the mechanical protection member and the displacement sensor winding. . 4. The eddy current displacement sensor according to claim 1, wherein the magnetic levitation support device is a magnetic bearing that levitationally supports a rotation shaft that is the object to be supported. Type displacement sensor.