JP2676359B2 - Position detector for magnetic bearings - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a position detecting device for a magnetic bearing, for example, in an ultra-vacuum spindle in which a rotor is magnetically levitated and supported by a magnetic bearing in vacuum. The present invention relates to a position detecting device for a magnetic bearing that detects the position of magnetic levitation in a non-contact manner.

[Prior Art] In a turbo molecular pump, several stages or dozens of stages of turbine blades are attached to a spindle shaft supported by rolling bearings and rotated at tens of thousands of rpm to obtain an ultrahigh vacuum.
Such turbo molecular pumps have recently been used in semiconductor manufacturing equipment. In this application, it is necessary to flow various trace gases on the surface of a semiconductor wafer for processing. Therefore, a pump that can operate under a wide range of vacuum conditions from medium vacuum to high vacuum is required.

FIG. 5 is a sectional view showing an example of a recent turbo molecular pump, and FIG. 6 is a view showing an example of a position sensor built in the turbo molecular pump.

First, the turbo molecular pump will be described with reference to FIGS. 5 and 6. In FIG. 5, the turbo molecular pump is covered with a case, which is the inner case 31.
And a lower outer case 32 and an upper outer case 33. The inner case 31 is formed as an inner hollow whose upper and lower ends are closed, and a flange 34 is formed in the middle outer periphery of the peripheral wall and a wiring passage 35 is formed in the lower portion.

Inside the inner case 31, there are a spindle shaft 36, and an upper radial magnetic bearing 37, a lower radial magnetic bearing 38, a thrust magnetic bearing 39 that supports the spindle shaft 36, and an upper radial magnetic bearing 37 and a lower radial magnetic bearing 38. Radial position sensors 40 and 41 for detecting the magnetic levitation position,
A motor 42 for rotating the spindle shaft 36 is housed. Emergency dry bearings 43, 44 are attached to the upper and lower ends of the inner case 31, and a thrust position sensor 45 for detecting the magnetic levitation position of the thrust magnetic bearing 39 is provided in the lower part of the inner case 31. Has been.

At the upper end of the spindle shaft 36 protruding from the inner case 31,
A fin rotor 47 having moving blades 46 provided on the outer periphery is detachably fixed, and a thread groove 49 for generating a low vacuum is provided on the outer periphery of a cylindrical portion 48 of the fin rotor 47.

The lower outer case 32 is formed on an upper surface opening into which the lower half part of the inner case 31 is fitted, and a power introducing terminal 50 and a non-reactive gas introducing hole 51 are provided in the lower part of the peripheral wall. The exhaust hole 52 provided in the upper part of the peripheral wall communicates with the passage 53 provided in the flange 34 of the inner case 31, and the exhaust port flange 54 is provided outside.

Inside the lower outer case 32, the space 55 connected to the power introduction part and the exhaust hole 52 are assembled so as to be fitted onto the inner case 31 between the fitting surfaces of the inner case 31 and the lower outer case 32. It is sealed by an O-ring 56. The non-reactive gas supplied from the introduction hole 51 into the space 55 flows into the inner case 31 from the passage hole 57 and the wiring passage 35 provided in the lower portion of the inner case 31 to fill the inner case 31. The non-reactive gas that has flowed out through the gap of the upper dry bearing 43 passes through the tubular portion 48 of the fin rotor 47 and the annular space of the inner case 31, and passes through the throttle portion 58 provided at the lower end of the tubular portion 48. After that, it flows out to the exhaust hole 52.

The narrowed portion 58 described above is effective by reducing the diameter of the inner diameter portion of the lower end of the tubular portion 48, but the inner case
It is also possible to configure by enlarging the outer diameter portion of 31.

The upper outer case 33 is formed in a tubular shape, and the lower end of the upper outer case 33 is externally fitted to the cylindrical wall 32a on the lower outer case 32, and this fitting portion is sealed by an O-ring 59, and the inner peripheral surface of the moving blade 46 The stator blades 60 facing each other and the stator 61 facing the screw groove 49 are attached. A ring-shaped notch 62 is provided in a portion of the fin rotor 47 that is attached to the spindle shaft 36.
The notch 62 is provided to prevent the fin rotor 47 from being subjected to centrifugal force by the rotation of the fin rotor 47, resulting in expansion of the fin rotor mounting portion and formation of a gap in the tapered portion. A suitable radius is provided at the bottom of the ring-shaped notch 62 to reduce stress concentration.

[Problems to be Solved by the Invention] Here, the radial position sensor 40 shown in FIG. 5 is required to detect the rotational axis displacement of the spindle shaft 36 in a non-contact manner. For this purpose, an eddy current type position detecting device 400 as shown in FIG. 6 is used as the radial position sensor 40.
The eddy current type position detecting device 400 is configured by winding an insulating coated thin copper wire 401 around a resin core several times to several tens of times in a ring shape to form a coil, and molding the outer peripheral portion of the coil with a resin. However, when such an eddy current type position detecting device 400 is used in a high vacuum, gas or the like may be generated from the mold resin. Therefore, it is necessary to take measures such as coating the coil with a stainless pipe. However, if the coil is covered with a stainless pipe, the whole becomes thicker, and the number of turns of the coil must be reduced in order to make it thinner. However, when the number of turns of the coil is reduced, the coil current increases for a constant load, so that the load capacity of the magnetic bearing becomes small when the power supply capacity is constant.

Therefore, a main object of the present invention is to provide a position detecting device for a magnetic bearing, which can detect a magnetic levitation position by utilizing a change in magnetic flux density of a magnetic loop formed by a permanent magnet without using an eddy current. Is.

[Specific Means for Solving the Problem] The invention according to claim 1 is that the outer diameter surface of a spindle fixed shaft provided with an electromagnet is covered with a non-magnetic member for sealing, and a rotor made of a magnetic body is fixed shaft. In a magnetic bearing device that rotates while being magnetically supported around, the magnetic bearing position detecting device for detecting the gap between the rotor and the spindle fixed shaft in a non-contact manner. A pair of yokes, which are provided so as to extend in a radial direction between the inner surface and the inner surface, are arranged so as to face each other with a predetermined gap in the axial direction, and the spindle fixed shaft side of each of the pair of yokes. A permanent magnet provided in the gap between the pair of yokes and a Hall element provided in the gap between the pair of non-magnetic members of the yokes for detecting a change in magnetic resistance caused by a change in the gap between the rotor and the spindle fixed shaft. It is comprised including.

According to a second aspect of the present invention, there is provided a magnetic bearing device in which an inner diameter surface of a housing of a spindle provided with an electromagnet is covered with a non-magnetic member for sealing, and a rotor made of a magnetic material rotates while being magnetically supported in the housing. A position detecting device for a magnetic bearing for detecting a gap between a rotor and a housing in a non-contact manner, the position detecting device for a magnetic bearing being provided on a housing so as to extend radially outward, each of which has a predetermined gap in the axial direction. And a pair of yokes provided to face each other
A permanent magnet provided on the side of the pair of yokes far from the rotor,
A pair of yokes is provided in the rotor-side gap, and a Hall element for detecting a change in magnetic resistance caused by a change in the gap between the rotor and the housing is configured.

[Operation] In the magnetic bearing position detecting device according to the inventions of claims 1 and 2, the magnetic bearing position detecting device having an outer rotor or an inner rotor and rotating, the magnetic flux generated by the permanent magnet provided in the yoke is generated by the yoke and the rotor. Since it passes through the magnetic circuit created, by detecting the change in magnetic resistance caused by the radial movement of the rotor by the Hall element,
The floating position of the rotor can be detected without contact.

[Embodiment of the Invention] FIG. 1 is a sectional view of an essential part of a vacuum spindle to which an embodiment of the present invention is applied.

First, the structure of a vacuum spindle to which an embodiment of the present invention is applied will be described with reference to FIG. The spindle shaft 1 made of a non-magnetic material is attached to the base 14. An electromagnet 2 for a motor for rotating the outer rotor 8 is provided substantially in the center of the spindle shaft 1, and electromagnets 3, 4 for magnetic bearings for magnetically levitating the outer rotor 8 are provided on both sides of the electromagnet 2 for the motor. In addition, sensors 5 and 6 for detecting a gap between the outer rotor 8 and the spindle shaft are provided. The periphery of the motor electromagnet 2, the magnetic bearing electromagnets 3 and 4, and the sensors 5 and 6 is covered with an aluminum case 7. One end of the aluminum case 7 is fixed to the base 14.

The inside of the aluminum case 7 is on the atmospheric pressure side. Then, the outer rotor 8 rotates while magnetically levitating around the aluminum case 7. The outer rotor 8 has a motor rotor 9 and a magnetic bearing rotor portion on its inner surfaces facing the motor electromagnet 2, the magnetic bearing electromagnets 3 and 4 and the sensors 5 and 6, respectively.
10, 11 and magnetic rings 12 and 13 are arranged.

In the vacuum spindle configured as described above, while the outer rotor 8 is magnetically levitated by the magnetic bearing electromagnets 3 and 4, the outer rotor 8 is rotated by the driving force of the motor electromagnet 2 and the gap between the spindle shaft is detected by the sensors 5 and 6. The electromagnetic force of the magnetic bearing electromagnets 3 and 4 is controlled by a control circuit (not shown).

2 is a sectional view taken along line II-II shown in FIG.
FIG. 3 is an enlarged view of a main part of the sensor.

Next, a sensor according to an embodiment of the present invention will be described with reference to FIGS. The sensor 5 includes yokes 501 to 508 divided into four in the circumferential direction.
˜504 and yokes 505 to 508 are arranged so as to face each other with a predetermined gap in the axial direction. That is, a yoke 505 for the yoke 501 and a yoke 506, a yoke 503 for the yoke 502.
On the other hand, the yoke 507 is arranged so that the yoke 508 faces the yoke 504, and the yoke 508 is arranged to face each other. These yokes 501 to 508 are attached to the insulating member 530 so as to be integrated, and are fixed to the spindle shaft 1. York 501-508
Of the permanent magnets 511 in the gaps on the spindle shaft 1 side of
~ 514 are mounted, and Hall elements 521 to 524 are mounted in the gaps between the yokes on the magnetic ring 12 side.

In the sensor 5 configured as described above, for example, the magnetic circuit A in which the magnetic flux generated in the permanent magnet 511 returns directly from the yoke 501 to the hall element 521 and returns to the permanent magnet 501 via the yoke 505, and the yoke 501 to the aluminum case 7. A magnetic circuit B is formed which passes through the magnetic ring 12 and passes through the aluminum case 7 again and returns to the yoke 505. And
The hall element 521 outputs a voltage according to the magnetic flux passing through the magnetic circuit A. Now, when the distance δ between the magnetic body ring 12 and the aluminum case 7 is large, among the magnetic fluxes generated by the permanent magnet 511, the magnetic flux passing through the magnetic circuit A increases, and the Hall element
The output voltage of 521 increases. On the contrary, when the interval δ is small, the magnetic flux passing through the magnetic circuit B increases, and the Hall element
The output voltage of 521 decreases.

That is, the magnitude of the magnetic resistance can be detected by the Hall element 521 depending on the size of the gap δ between the magnetic ring 12 and the aluminum case 7. Based on the detected output, the magnetic bearing shown in FIG. The interval δ can be controlled to a predetermined value by controlling the electromagnets 3 and 4.

FIG. 4 is a sectional view showing another example of a turbo molecular pump to which an embodiment of the present invention is applied.

The turbo molecular pump shown in FIG. 4 is of a so-called inner rotor type in which a rotor 78 is provided inside, and is constructed in substantially the same manner as the turbo molecular pump shown in FIG. That is, in the rotor 78, the motor rotor 79 is arranged on the peripheral surface of the central portion, and the magnetic bearing rotor portions 80, 81 and the magnetic material rings 82, 83 are provided on both sides of the motor rotor 79. An aluminum case 77 is provided so as to cover the rotor 78, a motor electromagnet 72 is arranged in a portion facing the motor rotor 79, and a magnetic bearing electromagnet 73, in a portion facing the magnetic bearing rotor portions 80, 81. 74 is arranged, and sensors 75 and 76 are provided so as to face the magnetic rings 82 and 83. The outside of the aluminum case 77 is at atmospheric pressure.

The sensors 75 and 76 are constructed in substantially the same manner as shown in FIGS. 2 and 3 above, but in this embodiment,
Permanent magnets 751 and 761 are provided in the part far from the rotor 78,
The hall elements 752, 762 are provided on the rotor 78 side. As described above, even if the inner rotor type turbo molecular pump is configured, the gap between the rotor 78 and the aluminum case 77 can be satisfactorily detected.

As described above, according to the present invention, the magnetic flux generated by the permanent magnet provided in the yoke passes through the magnetic circuit formed by the yoke and the rotor, and the magnetic resistance generated by the change in the clearance between the rotor and the spindle shaft. By detecting the change of the above with the Hall element, it is possible to detect the floating position of the rotor in a non-contact manner without using the eddy current as in the prior art.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a turbo molecular pump to which an embodiment of the present invention is applied. FIG. 2 is a sectional view taken along the line II-II shown in FIG. FIG. 3 is a sectional view showing the main part of one embodiment of the present invention. FIG. 4 is a sectional view showing another example of a turbo molecular pump to which an embodiment of the present invention is applied. FIG. 5 is a sectional view showing the structure of a turbo molecular pump which is an application example of a conventional vacuum spindle. FIG. 6 is a diagram showing an example of a conventional position sensor using the eddy current method. In the figure, 1 is a spindle shaft, 2,72 is a motor electromagnet, 3,4,73,74 are magnetic bearing electromagnets, 5,6,75,76 are sensors, 7,77 is an aluminum case, 8 is an outer rotor, 12,13,8
2,83 magnetic ring, 78 rotor, 501-508 yoke,
511 to 514,751,761 are permanent magnets, 521 to 524,752,762 are Hall elements, and 530 is an insulating member.

Claims (2)

(57) [Claims] 1. A magnetic bearing device in which an outer diameter surface of a spindle fixed shaft provided with an electromagnet is covered with a non-magnetic member for sealing, and a rotor made of a magnetic material rotates while being magnetically supported around the fixed shaft. In a magnetic bearing position detecting device for detecting the gap between the rotor and the spindle fixed shaft in a non-contact manner, the position detecting device extending in the radial direction between the spindle fixed shaft and the inner surface of the non-magnetic member. And a pair of yokes arranged so as to face each other with a predetermined gap in the axial direction, permanent magnets provided in gaps on the spindle fixed shaft side of the pair of yokes, respectively, and A Hall element is provided in a gap between the pair of yokes on the side of the non-magnetic member to detect a change in magnetic resistance caused by a change in a gap between the rotor and the spindle fixed shaft. Example was, the position detecting device for a magnetic bearing. 2. A magnetic bearing device in which an inner diameter surface of a housing of a spindle equipped with an electromagnet is covered with a non-magnetic member for sealing, and a rotor made of a magnetic material rotates while being magnetically supported in the housing. A magnetic bearing position detecting device for detecting a gap between a rotor and the housing in a non-contact manner, wherein the position detecting device is provided on the housing so as to extend radially outward, and each has a predetermined gap in the axial direction. And a pair of yokes provided so as to face each other, a permanent magnet provided on a side of the pair of yokes far from the rotor, and a pair of yokes provided on a gap between the pair of yokes on the rotor side. With a Hall element for detecting the change in magnetic resistance caused by the change in the gap to the housing,
Position detector for magnetic bearings.