KR19990064661A - Cylindrical capacitive sensor of magnetic bearing - Google Patents

Abstract

Disclosed is a displacement sensor of a magnetic bearing mounted on a magnetic bearing to minimize a shape error by improving a dividing angle of a capacitive sensor measuring displacement. Such a displacement sensor of a magnetic bearing, the capacitive displacement sensor of the circular plate which is embedded in the magnetic bearing module for measuring the displacement, comprising: a cylindrical body having a predetermined inner diameter for measuring the displacement of the magnetic bearing; It is composed of eight divisions so as to maintain a constant gap with each other inside the body, and the division angle is repeatedly provided at 60 degrees and 30 degrees, and each has a sensor unit that can be combined with each other. Realizing a shape having a combination of 120 degrees, and is provided between the sensor portion and the body further comprises a cylindrical guard surrounding the entire circumference to open the upper side of the sensor portion. Therefore, assuming that the axial shape error is a periodic function in which several cycles are combined, it is possible to eliminate the shape error of a specific period as the dividing angle of the sensor is changed, particularly when the above-mentioned eight division angles are obtained. The displacement of the rotating shaft can be measured and the measurement noise due to the shape error can be reduced.

Description

Displacement sensor of magnetic bearing {Cylindrical capacitive sensor of magnetic bearing}

The present invention relates to a displacement sensor of a magnetic bearing to minimize the shape error by improving the divided angle of the cylindrical capacitance displacement sensor mounted on the magnetic bearing to measure the displacement.

In general, the non-contact displacement sensor used to measure the displacement generated during rotation of the shaft is an optical sensor using the interference effect of the reflected light according to the medium used for position measurement, a laser sensor using the reflected wave of the laser beam, conductive metal object The eddy current sensor converts the impedance change in the sensor coil due to the eddy current generated from the surface into a displacement, and the capacitance sensor that measures the distance from the magnitude of the capacitance formed between the conductive object and the sensor plate.

However, among these kinds of non-contact displacement sensors, a sensor mounted on a magnetic bearing and capable of measuring the displacement of the rotating shaft is very limited. This is because the installation space of the magnetic bearing, the shape of the sensor, and the Its use is limited due to influence and the like.

Eddy current-driven displacement sensors are most commonly used for displacement measurement of rotating shafts in magnetic bearings because they are inexpensive and easy to install and use.

However, because the eddy current driven displacement sensor is affected by the magnetic field, it should be installed at least 25.4mm from the pole of the stator core. Therefore, the working position and the measuring position of the magnetic bearing are inconsistent and the magnetic bearing in the higher order mode of the flexible shaft There was a problem of this becoming unstable.

In addition, since displacement sensors generally measure only one point of the journal surface, the movement error and surface roughness of the journal are mixed with the measured displacement signal, and thus the exact position change of the journal geometric center cannot be measured.

This position measurement error is introduced into the control operation of the magnetic bearing controller as it acts as a disturbing factor, which causes a problem of making it difficult to accurately control the magnetic bearing.

In addition, the displacement measuring system using a non-contact displacement measuring sensor is not only expensive equipment, but also has a problem in that its installation and use is inconvenient.

Therefore, in order to solve the conventional problems as described above, the 'magnetic bearing and its manufacturing method' in which the capacitance sensor is embedded in the magnetic bearing is described in Patent Application No. 94-33038.

Such a magnetic bearing and its manufacturing method are as follows with reference to FIG.

Reference numeral 10 denotes a stator core, and the stator core 10 is manufactured by stacking about 40 to 60 sheets of core plates press-processed with thin silicon plates in order to prevent heat generation due to eddy current generation.

Reference numeral 30 denotes a cylindrical capacitance sensor made of brass, and the capacitance sensor 30 is adhered to the upper surface of the poles (not shown) to be electrically insulated.

Here, an insulating ring 12 having a thickness of about 1 mm is interposed between the poles of the stator core 10 and the capacitance sensor 30 for electrical insulation.

The capacitance sensor 30 is composed of four sensor plates 31 and guard plates 32, each of which has a constant gap therebetween and is separated from each other.

The sensor plate 31 and the guard plate 32 of the capacitance sensor 30 are disposed at an angle of 90 degrees with respect to two directions of vertical and horizontal, and the areas of the sensor plate 31 and the guard plate 32 are equal to each other. It is.

Reference numerals 40 and 41 denote sensor wires and guard wires of the capacitance sensor 30, the sensor wires 40 are respectively wired to the sensor plates 31, and the guard wires 41 are wired to the guard plates 32, respectively. do.

These sensors and guard wires 40 and 41 are all used in a shielded form and are twisted and twisted in a mesh form to cross in opposite directions.

Accordingly, the sensor and guard wires 40 and 41 cancel each other by turning in opposite directions, and eight sensors and guards in all sections from the sensor and guard plates 31 and 32 to the sensor amplifiers (not shown). Lines 40 and 41 can both maintain the same ground level and noise level.

However, such a magnetic bearing and its manufacturing method have the following problems.

First, since the stator core poles and the sensor are integrally impregnated using the polycoat, the polycoat is deformed by the vibration of the coil generated when the magnetic bearing is operated.

Second, since there is no solid reference plane in the inner diameter grinding of the magnetic bearing module and the outer diameter grinding of the stator core, it is difficult to obtain the desired concentricity.

Third, since it consists of four sensor plates with a 90 degree dividing angle, even-numbered periodic shape errors can be eliminated by the differential arrangement, but since the dividing angle of the sensor cannot be changed, it is possible to eliminate the shape errors of specific periods. In particular, there is a problem that is very vulnerable to three-cycle shape error, which greatly affects the rotational accuracy of the axis.

Fourth, the magnetic bearing is a real-time control system, so it should be designed to have stability in case of a problem during operation. The stability of the magnetic bearing system is unstable, even if only one of the four sensor plates occurs. Can cause serious problems.

Accordingly, an object of the present invention, which is created to solve the problems of the conventional four-piece cylindrical capacitive displacement sensor used in magnetic bearings as described above, is to improve the division angle of the capacitive displacement sensor and to generate a specific period during displacement measurement. The present invention provides a displacement sensor of a magnetic bearing that enables accurate measurement by reducing the measurement noise caused by the shape error.

In addition, another object of the present invention, by implementing a shape having an arbitrary division angle to configure the two differential sensor combinations displacement of the magnetic bearing to enable a stable operation with an extra sensor combination even if there is an abnormality in one sensor combination In providing a sensor.

1 is a perspective view showing a coupling and wiring state of a capacitive displacement sensor in a conventional magnetic bearing;

2 is a perspective view of a magnetic bearing module including a displacement sensor of a magnetic bearing according to the present invention;

3 is a cross-sectional view of the displacement sensor of the magnetic bearing according to the present invention;

4 is an exploded perspective view of a displacement sensor of a magnetic bearing according to the present invention;

Figure 5 (a) is a perspective view of a sensor unit according to the present invention,

Figure 5 (b) is a perspective view of the guard according to the present invention,

Figure 5 (c) is a perspective view of the body according to the present invention,

Figure 6 (a) is a cross-sectional view showing the assembly process of the displacement sensor according to the present invention,

Figure 6 (b) is a cross-sectional view showing the final processing shape of the displacement sensor according to the present invention,

7 is a configuration diagram of an experimental apparatus for measuring shape errors using the present invention;

8 (a) and (b) are schematic views of a test axis according to the present invention;

Figure 9 (a) (b) is a graph showing the shape error of the test axis according to the present invention for each period,

Figure 10 (a) (b) (c) is a graph of the experimental results of the conventional four-piece cylindrical sensor and the eight-piece cylindrical sensor according to the present invention.

Explanation of symbols for main parts of the drawings

50 ... displacement sensor 51 ... sensor

52 ... Guard 53 ... Body

Displacement sensor of the magnetic bearing according to the present invention for achieving the above object, in the capacitive displacement sensor of the circular plate which is embedded in the magnetic bearing module to measure the displacement, a cylindrical having a predetermined inner diameter for measuring the displacement of the magnetic bearing With the body of; It is made of eight divisions so as to maintain a constant void from each other inside the body, the division angle is characterized in that it is repeatedly provided with a sensor unit capable of performing a mutually merge operation is provided at 60 degrees and 30 degrees.

The above-described sensor unit is used by overlapping 30 degrees, thereby realizing a shape having 120 degrees having two differential sensor combinations.

In addition, provided between the sensor portion and the body further comprises a cylindrical guard surrounding the entire circumference to open the upper side of the sensor portion.

According to the characteristics of the present invention as described above, the displacement sensor of the magnetic bearing according to the present invention, assuming that the axial shape error as a periodic function of the sum of several cycles, the shape error of a specific period as the split angle of the sensor is changed As it can be removed, the measurement noise due to the shape error can be reduced, thereby enabling precise measurement and control of the rotating shaft.

In addition, since the combination of the two sensors can increase the stability of the magnetic bearing, the performance of the magnetic bearing can be significantly improved.

Hereinafter, a preferred embodiment of a displacement sensor of a magnetic bearing according to the present invention will be described in detail with reference to the accompanying drawings.

2 to 6, the displacement sensor of the magnetic bearing according to the present invention is as follows.

First, in order to obtain stable performance, an active magnetic bearing always supports the shaft through control using a positioning signal.

The performance of these magnetic bearings is directly influenced by how accurate the signal of the position sensor is, and the accuracy of the displacement sensor is mainly determined by the resolution and shape error of the shaft.

In high speed precision spindles and coarse precision machines, it is particularly important to eliminate shaft shape errors because signals caused by shaft shape errors cause severe vibrations in magnetic bearing control.

The displacement sensor of the magnetic bearing according to the present invention for removing the above-described shape error is as follows.

2 is a perspective view of the magnetic bearing module 70, which is largely comprised of a sensor 50 and an electromagnet actuator 60. As shown in FIG.

The sensor unit 51 and the guard 52 are assembled by epoxy impregnation to the sensor body 53 to form the sensor 50, and the magnetic core 61 and the coil 62 made of a laminated thin silicon steel sheet are electromagnet actuators. It is coupled to the body 63 to form an electromagnet actuator 60.

Therefore, the sensor 50 can be prevented from being deformed by the vibration of the coil 62 by separating the sensor 50 from the electromagnet actuator 60.

Such, the sensor 50 and the electromagnet actuator 60 is permanently coupled by applying a constant pressure by the bolt when the silicon steel sheet is laminated, the solid magnetic coupling module 70 is thus firmly coupled to the sensor 50 and the electromagnet actuator 60 ) Is integrated into the inner diameter machining, it can minimize the concentricity error that can be a problem when measuring and controlling.

Figure 3 is a cross-sectional view of the capacitive displacement sensor 50 according to the present invention is composed of eight sensor parts 51 and the guard 52 are separated from each other to maintain a constant gap.

The division angles of the eight sensor parts 51 are divided into 60 degrees, 30 degrees, 60 degrees, 30 degrees, 60 degrees, 30 degrees, 60 degrees, and 30 degrees, respectively, and the capacitance measurement values of the corresponding sensor plates are respectively C1C2. When represented by C8, the displacement of the axis of rotation is measured as X = (C8 + C1 + C2)-(C4 + C5 + C6), Y = (C2 + C3 + C4)-(C6 + C7 + C8) and 30 Since the part of the diagram is used redundantly, it actually has a sensor size of 120 degrees.

The advantage of having these eight sensor plates is that first, the angle of the sensor plate can be adjusted to realize an arbitrary dividing angle, and the dividing angle of the displacement sensor can be reduced to 120 degrees to minimize the influence of the shape error of the rotating shaft. Is the point.

In addition, since four sensor plates are required for one sensor combination, the sensor can have two sensor combinations. In this case, each sensor combination includes a sensor combination consisting of C1, C3, C5, and C7, and C2, C4, and C6. It is a sensor combination consisting of C8, and it is possible to maintain stable operation with an extra sensor combination even when a problem occurs in any sensor plate during magnetic bearing operation.

In addition, although the ideal angle may be slightly different at 120 degrees due to the inevitably required air gap for insulation between the sensor plates, this angle error can be compensated by a simple equation. It is possible to implement a sensor having a desired dividing angle, the angle error is compensated for.

The mathematical interpretation of this 8-segment cylindrical capacitive displacement sensor is as follows.

E = sin (mz) / msin (z) ..... Equation (1)

Equation (1) shows the characteristics of the shape error included in the measured value of the cylindrical capacitive displacement sensor, where m represents the period of the shape error, and the even period is naturally eliminated by the differential arrangement, and therefore, odd (3) , 5, 7, ....) cycles only, z represents the size of the sensor in degrees.

As can be seen from Equation (1), in the case of a sensor (z = 90 degrees) that makes full use of the sensor area, the measurement error is the inverse of the cycle, that is, 1/3, 1/5, 1/7, 1/9 It becomes ...

Therefore, it is the most vulnerable to the shape error for the axis containing the three-cycle shape error.

However, if the sensor size (ζ) is 60 degrees, the measurement error appears as 0, 1/5, 1/7, 0 ... for each period, so that the most influential three-cycle shape error can be eliminated. In addition, other periods of multiples of three can also be eliminated, significantly increasing measurement accuracy.

Therefore, the measurement error can be minimized by using the new arrangement as shown in FIG.

When the sensor uses a smaller area of 120 degrees than the total circumference of 180 degrees, the shape error elimination effect is increased.

4 is an exploded perspective view of the displacement sensor, a guard 52 made of brass and a guard 53 embedded in the body 53, and a body 53 surrounding the guard 52. It is configured, the sensor unit 51 and the guard 52, the body 53 are all coupled while maintaining concentricity.

Reference numerals 50a and 50b denote sensor lines 50a and guard lines 50b of the capacitive sensor 50, the sensor lines 50b are wired to the sensor portions 51, respectively, and the guard lines 50b are guards ( 52).

Since there are eight sensor plates of the sensor unit 51, one is wired to each sensor plate, and the eight strands thus wired are twisted into a mesh to form a single wire.

The sensor wires 50b are twisted in a mesh shape to be alternately twisted in opposite directions, and are shielded by the guard wires 50a in order to reduce the influence of parasitic capacitance to the wiring holes 53a of the body 53. It is coupled to a connection jack (not shown) located.

This connecting jack (not shown) is electrically connected to the body 52 and connected to a ground wire (not shown) of an external power source. Since the ground wire is shielded while surrounding the guard wire, the wiring of the displacement sensor is totally 10 3 It has the form of a coaxial line.

5A to 5C are views showing the structure of the displacement sensor.

According to FIG. 5A, the sensor part 51 has a cylindrical auxiliary surface 51a formed in one direction to be coupled concentrically to the guard 52, and below the locking jaw for insulation from the guard 52. 51b is formed, and the sensor plates 51c are located below the locking step 51b.

On the sensor surface, in order to separate the sensor plate 51c into eight and to insulate each other, the linear insulating grooves 51d are formed perpendicular to the outer circumferential surface, and the circumference along the outer circumferential surface to hold the positions of the respective sensor lines 50b. The wiring groove 51e is formed also in the direction.

Fig. 5B shows the integrated guard 52, the upper side of which is open for easy assembly, and a cylindrical auxiliary surface 52a formed in one direction to maintain concentricity when assembled with the body 53, Underneath, the locking jaw 52b is formed to maintain the insulation of the body 53.

In addition, a discharge groove 52c is formed to wire the guard wire 50a and to provide a place for the sensor wires 50b to pass through.

FIG. 5C shows a body 53 to which the sensor unit 51 and the guard 52 are coupled, and has a wiring hole 53a on one side so that a connection jack (not shown) for wiring is coupled.

The assembly process and final processing method of the present invention made up of these components will be described with reference to FIGS. 6A and 6B.

First, as shown in FIG. 6A, the sensor unit 51 and the guard 52 are seated on the body 53 and impregnated with epoxy, and then the assembled sensor 50 is permanently coupled with the electromagnet actuator 60 again.

Thereafter, when the inner diameter is processed to a certain depth as shown in FIG. 6B, the sensor unit 51, the guard 52, and the body 53 are separated and insulated from each other.

In the experimental apparatus for measuring the shape error of such a sensor, referring to FIG. 7, one side of the shaft was supported by a hydrostatic bearing (400), and the other side was an oilless bearing (100) to move a position. The rotation radius of the shaft is adjusted by changing the position and rotation speed of the bearing.

In addition, an eight-piece cylindrical capacitive displacement sensor (CCS) and a four-piece cylindrical capacitive displacement sensor (CCS) were combined side by side in an experimental housing 200 equipped with a cylindrical capacitive displacement sensor (CCS). In order to compare the shape error removal performance of the sensor with the probe-type sensor, a probe-type sensor 300 was mounted.

In order to prove the shape error of the sensor and the performance of the new sensor, the axis with a certain period of shape error should be used. Since it is almost impossible to realize the shape error with real precision, a new type of test axis as shown in FIG. Prepared.

8 (a) is a test axis for implementing a drainage period of 3, and FIG. 8 (b) is a test axis for implementing a shape error of the drainage period of 4, that is, an even period.

The reason for verifying the performance of the sensor with only these test axes is not the absolute value of the shape error or the rotation radius of the axis, but the ratio when the actual analysis results are important. Therefore, when the shape error is large, increase the rotation radius of the axis. This is because the characteristics at that time may be investigated.

However, since the equation must be δh in the assumption that the mathematical equation is valid, h must be within 50 μm in consideration of δ = 0.5 mm.

9 (a) and 9 (b) show the shape errors of the test axes of FIG. 8 described above for each period.

As can be seen in FIG. 9, since the test axes include all the cycles, if the shape errors in the test axes can be eliminated, it means that the shape errors of all the cycles can be eliminated.

Comparing the four-piece cylindrical sensor and the eight-piece cylindrical sensor by this experiment, it is as shown in Fig. 10 (a) (b) (c).

Fig. 10 (a) shows when the axis rotates at 20 μm, Fig. 10 (b) shows when the axis rotates at 10 μm, and Fig. 10 (c) shows when the axis rotates at 5 μm.

Accordingly, the cylindrical sensor can eliminate the shape error due to the averaging effect, and the newly designed eight-piece sensor can remove the shape error more sensitively than the conventional four-piece cylindrical sensor.

In the case of the probe type sensor measuring the distance at one point, the shape error remains as it is, so the position of the actual axis center cannot be known well, but in the case of the cylindrical sensor, the rotational trajectory of the actual axis center is shown as it is regardless of the shape error.

In the case of four-piece sensor that is payable at 90 degrees, the more accurate the rotation trajectory is, the more the rotational trajectory is distorted due to the three-cycle shape error. However, in the case of the newly designed eight-piece sensor, the measurement signal appears closer to the actual trajectory.

Therefore, the present invention can be applied even in the case of an ultra-precision spindle which requires more than the shape error of the axis.

As described above, the displacement sensor of the magnetic bearing according to the present invention has the following effects.

First, by improving the split angle of the capacitive displacement sensor, it is possible to precisely measure by reducing the measurement noise caused by the shape error of a specific period generated during the displacement measurement to the maximum.

Second, since two differential sensor combinations are configured by implementing a shape having an arbitrary dividing angle, even if an error occurs in one sensor combination, an extra sensor combination enables stable operation.

Third, since a shape having an arbitrary angle can be implemented, when the error due to the sensor interval is considered, the error can be compensated by a simple equation.

Claims (3)

In the capacitive displacement sensor of the circular plate which is embedded in the magnetic bearing module to measure the displacement, A cylindrical body having a predetermined inner diameter for measuring displacement of the magnetic bearing; Comprising eight divisions so as to maintain a constant void from each other inside the body, the displacement angle of the magnetic bearing, characterized in that the divided angle is repeatedly provided with a sensor unit capable of mutually combined operation is provided at 60 degrees and 30 degrees. The displacement sensor of a magnetic bearing according to claim 1, wherein the sensor unit is overlapped with 30 degrees to realize a shape having 120 degrees having a combination of two differential sensors. The displacement sensor of a magnetic bearing according to claim 1 or 2, further comprising a cylindrical guard provided between the sensor unit and the body and surrounding the entire circumference such that an upper side of the sensor unit is opened.