JP2008038935A - Bearing device and turbo molecular pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a magnetized inner ring from being dragged, in a protection bearing provided with a rolling element comprising a nonmagnetic substance. <P>SOLUTION: The inner ring 41 and an outer ring 42 are formed of members each comprising a magnetic substance, and the rolling element 43 is formed of a nonmagnetic substance. A magnetic guide body 44 is a member formed of a magnetic material, and provided with a magnetic guide mechanism for guiding the magnetism of the magnetized inner ring to a closed magnetic path passing the inner ring and the outer ring. A magnetic guide part 44b is constituted of a portion overhung from the inner circumferential edge of a bearing fixing part 44a toward the extension direction of a bearing fixing part and an axial direction, and contacts with the outer ring to reduce magnetic resistance. A space β of a clearance between the inner ring of the protection bearing and the magnetic guide part is constituted to be sufficiently small compared with a space α of a clearance between the inner circumferential face of the inner ring and the outer circumferential wall face of a shaft 7. Many-pieces magnetic flux are picked up by providing the magnetic guide body to satisfy a relation of the space β<the space α so as to be guided to the closed magnetic path passing the inner ring and the outer ring. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bearing device and a turbo molecular pump that support a rotating shaft in a non-contact manner, and more particularly to a bearing device and a turbo molecular pump provided with a protective bearing (auxiliary bearing) that backs up at the time of touchdown.

In a bearing device that supports a rotating shaft in a non-contact manner, such as a hydrodynamic bearing device or a magnetic bearing device, it is structurally difficult to obtain a large (high) rigidity of the device.
For this reason, such non-contact bearing devices are equipped with emergency (protective) protective bearings (touch-down bearings) in the event of disturbances such as earthquake impacts or abnormalities in the control system. ing.
And when it becomes a state which cannot hold | maintain a rotating shaft by non-contact, it is comprised so that it may back up with this protection bearing.
In addition, the protective bearing is comprised by rolling bearings, such as a ball bearing and a roller bearing, for example.

Since the load is not applied to the protective bearing (auxiliary bearing) while the rotating shaft is supported in a non-contact manner, the inner ring (contact wheel with the rotating shaft) of the protective bearing is stopped.
However, when the bearing device is in a non-contact state and cannot hold the rotating shaft, that is, when the protective bearing functions, the inner ring of the protective bearing contacts the rotating shaft and is close to the rated rotational speed (rotor rotational speed). It is accelerated rapidly.
For this reason, the rolling elements (balls, rollers) of the protective bearing are light weight and have a small rotational torque, such as a ceramic member.

By the way, there is a turbo molecular pump that uses such a non-contact bearing to exhaust gas by the action of a fixed blade and a rotating blade rotating at high speed.
The turbo molecular pump uses a high-frequency motor to rotate the rotor blades at high speed. Therefore, the permanent magnet which comprises a high frequency motor is embed | buried in the rotating shaft.
When assembling such a turbo molecular pump, generally, a rotating shaft is inserted into a cylindrical fixing portion having a protective bearing at its end.
For this reason, when the permanent magnet embedded in the rotating shaft passes through the inside of the protective bearing, the race rings (inner ring, outer ring) of the protective bearing are magnetized.

FIG. 9 is a view showing a state in which the race is magnetized in the conventional protective bearing. 9A shows a cross section in the radial direction (radial direction) of the protective bearing, and FIG. 9B shows a cross section in the axial direction (axial direction).
When the bearing ring of the protective bearing is magnetized, as shown in FIG. 9, a closed magnetic circuit (thick line) passing through the inner ring 101 and the rotating shaft 104 and a closed magnetic circuit (broken line) passing through the inner ring 101 and the outer ring 102, that is, a magnetic circuit Is formed.
However, since the rolling element 103 is composed of a non-magnetic member (for example, a ceramic member), the gap between the inner ring 101 and the outer ring 102 functions as an air gap as between the inner ring 101 and the rotating shaft 104. To do.
Therefore, the magnetic flux density in the magnetic circuit is larger (higher) in the closed magnetic path (thick line) passing through the inner ring 101 and the rotating shaft 104 than in the closed magnetic path (broken line) passing through the inner ring 101 and the outer ring 102.

When the bearing ring of the protective bearing is magnetized, the inner ring 103 of the protective bearing is not attached to the rotating shaft 104 even when the rotating shaft 104 is supported in a non-contact manner due to the interaction with the rotating shaft 104. As it rotates, it rotates (takes around).
Specifically, an induced current is generated inside the rotating shaft 104 due to the magnetism of the race (inner ring 101). As a result, the inner ring 101 of the protective bearing rotates by attracting the magnetic force generated by the rotating shaft 104.

If such rotation of the inner ring 101 occurs, the life of the protective bearing may be reduced. Further, when the inner ring 101 is rotated, noise and vibration due to the rotation of the inner ring 101 may be a problem.
Therefore, conventionally, a method for preventing the rotation of the bearing ring in a protective bearing using such a non-magnetic rolling element has been proposed in the following patent documents.
JP 2002-54593 A

Patent Document 1 proposes a technique in which an inner ring of a touch-down bearing (protective bearing) is formed of a material having a low residual magnetic flux density, and the inner ring is prevented from being magnetized.
Specifically, there has been proposed a technique for suppressing the inner ring of the touchdown bearing from being magnetized by forming the inner ring of the touchdown bearing with a nonmagnetic member such as austenitic stainless steel formed in a solid state. Yes.

However, as proposed in Patent Document 1, when the inner ring is made of a non-magnetic member, the non-magnetic member has low rigidity, so that the strength (rigidity) of the protective bearing (touch-down bearing) is sufficiently high. It was difficult to hold.
Then, an object of this invention is to provide the bearing device provided with the protection bearing which can suppress appropriately the accompanying rotation of an inner ring | wheel while maintaining sufficient rigidity, and a turbo-molecular pump.

According to the first aspect of the present invention, there is provided a bearing device that supports a rotating shaft on which a permanent magnet constituting a motor is disposed in a non-contact manner, and forms a rolling element made of a non-magnetic material and a track of the rolling element. And a protective bearing that supports the rotating shaft at the time of stop and abnormal condition, and the protective bearing has a magnetic induction structure that makes the rotational torque of the inner ring smaller than the friction torque. This achieves the object.
Note that the rotational torque of the inner ring indicates, for example, traction torque that rotates with the rotation of the rotation shaft.
In the first aspect, for example, it is preferable that the magnetic resistance between the inner ring and the outer ring is smaller than the magnetic resistance between the inner ring and the rotating shaft.
According to a second aspect of the present invention, in the bearing device according to the first aspect, the magnetic induction structure comprises a magnetic induction member made of a magnetic member for guiding the magnetism of the inner ring to the outer ring. .
According to a third aspect of the present invention, in the bearing device according to the second aspect, the magnetic induction member is disposed with a predetermined distance β between the inner ring and the distance β between the rotating shaft and the inner ring. It is characterized by being smaller than the interval α.
According to a fourth aspect of the present invention, in the bearing device according to the first, second, or third aspect, the magnetic induction structure is configured such that a distance γ between the inner ring and the outer ring is set between the rotating shaft and the inner ring. It is characterized by being configured to be smaller than the interval α.
According to a fifth aspect of the present invention, in the bearing device according to the first, second, third, or fourth aspect, the rolling element is made of a ceramic member.
According to a sixth aspect of the present invention, in the bearing device according to any one of the first to fifth aspects, the rotating shaft is supported by a magnetic force or a dynamic pressure.
According to a seventh aspect of the present invention, there is provided a turbomolecular pump comprising the bearing device according to any one of the first to sixth aspects.

  According to the present invention, the accompanying rotation of the inner ring can be suppressed by providing the magnetic induction structure that makes the rotational torque of the inner ring in the protective bearing smaller than the friction torque.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
In this embodiment, a turbo molecular pump provided with a magnetic bearing device will be described as a device using a non-contact bearing device having a protective bearing.
In the present embodiment, a description will be given using a composite turbo molecular pump having a turbo molecular pump portion T and a thread groove pump portion S as an example of a turbo molecular pump.

FIG. 1 is a diagram showing a schematic configuration of a turbo molecular pump 1 according to the present embodiment. FIG. 1 shows a cross section in the axial direction of the turbo molecular pump 1. This turbo molecular pump is installed, for example, in a semiconductor manufacturing apparatus, and is used when exhausting process gas from a vacuum chamber.
The casing 2 constituting the exterior body of the turbo molecular pump 1 has a substantially cylindrical shape, and forms the casing of the turbo molecular pump 1 together with the base 3 provided at the lower part of the casing 2 (exhaust port 6 side). ing. A structure for causing the turbo molecular pump 1 to perform an exhaust function, that is, a gas transfer mechanism is disposed inside the housing.

This gas transfer mechanism is roughly composed of a rotating part that is rotatably supported and a fixed part fixed to the casing.
An inlet 4 for introducing gas into the turbo molecular pump 1 is formed at the end of the casing 2. A flange portion 5 is formed on the end surface of the casing 2 on the intake port 4 side so as to project to the outer peripheral side.
The base 3 is formed with an exhaust port 6 for exhausting gas from the turbo molecular pump 1, that is, exhausting process gas from the semiconductor manufacturing apparatus.

The rotating part includes a shaft 7 as a rotating shaft, a rotor body 8 having a substantially U-shaped cross section disposed on the shaft 7, a rotor blade 9 provided on the rotor body 8, and the exhaust port 6 side (screw groove pump part) S), and the like.
The rotor body 8 is fixed to the upper part of the shaft 7 with bolts 23. The cylindrical member 10 is formed on the extension of the rotor body 8 and is formed of a cylindrical member concentric with the rotation axis of the rotor body 8.
A rotor blade 9 is disposed on the outer periphery of the rotor body 8, and the rotor blade 9 is formed by blades (blades) extending radially from the shaft 7 at a predetermined angle with respect to a plane perpendicular to the axis of the shaft 7. Become.

A motor part 11 for rotating the shaft 7 at a high speed is provided in the middle of the shaft 7 in the axial direction. The motor unit 11 is a DC brushless motor (high frequency motor), and is configured as follows.
The motor unit 11 includes a permanent magnet 111 embedded in the shaft 7. For example, the permanent magnet 111 is fixed so that the N pole and the S pole are arranged around the shaft 7 every 180 °.
In addition, the motor unit 11 includes an electromagnet 112 disposed around the permanent magnet with a predetermined clearance from the shaft 7. Here, six electromagnets are disposed so as to be symmetrically opposed to the axis of the shaft 7 every 60 °.

The turbo molecular pump 1 is connected to the control device 70 via a connector and a cable. Then, the current of the electromagnet 112 is switched one after another so that the rotation of the shaft 7 is continued by the control device 70.
That is, the control device 70 generates a rotating magnetic field around the permanent magnet 111 fixed to the shaft 7 by switching the excitation currents of the six electromagnets 112, and causes the shaft to move by causing the permanent magnet 111 to follow the rotating magnetic field. 7 is rotated.

Magnetic bearings 12 and 13 for pivotally supporting the shaft 7 in the radial direction (radial direction) are provided on the intake port 4 side and the exhaust port 6 side with respect to the motor portion 11 of the shaft 7.
In addition, a magnetic bearing 14 for supporting the shaft 7 in the thrust direction (axial direction) is provided at the lower end (exhaust port side end) of the shaft 7.
These magnetic bearings 12 to 14 constitute so-called five-axis control type magnetic bearings.
The shaft 7 is supported by the magnetic bearings 12 and 13 in a non-contact manner in the radial direction (the radial direction of the shaft 7), and is supported by the magnetic bearing 14 in a non-contact manner in the thrust direction (the axial direction of the shaft 7).
Displacement sensors 15 to 17 for detecting the displacement of the shaft 7 are provided in the vicinity of the magnetic bearings 12 to 14, respectively.

Four electromagnets are arranged on the magnetic bearing 12 so as to face the periphery of the shaft 7 every 90 °. The shaft 7 is formed of a high permeability material (iron or the like) and is attracted by the magnetic force of these electromagnets.
The displacement sensor 15 samples and detects the radial displacement of the shaft 7 at predetermined time intervals.

When the control device 70 detects that the shaft 7 is displaced from the predetermined position in the radial direction by the displacement signal from the displacement sensor 15, the control device 70 adjusts the magnetic force of each electromagnet in the magnetic bearing 12 to bring the shaft 7 into the predetermined position. Operate to return. The adjustment of the magnetic force of the electromagnet is performed by feedback controlling the excitation current of each electromagnet.
The control device 70 performs feedback control of the magnetic bearing 12 based on the signal from the displacement sensor 15, whereby the shaft 7 is magnetically levitated in the radial direction with a predetermined clearance from the electromagnet in the magnetic bearing 12, and is not in the space. Held in contact.

The configuration and operation of the magnetic bearing 13 are the same as those of the magnetic bearing 12. The control device 70 performs feedback control of the magnetic bearing 13 based on the signal of the displacement sensor 16, whereby the shaft 7 is magnetically levitated in the radial direction by the magnetic bearing 13 and is held in a non-contact manner in the space.
Thus, the shaft 7 is held at a predetermined position in the radial direction by the action of the magnetic bearings 12 and 13.

The magnetic bearing 14 includes a disk-shaped metal disk 18 and electromagnets 19 and 20, and holds the shaft 7 in the thrust direction.
The metal disk 18 is made of a high permeability material such as iron, and is fixed perpendicularly to the shaft 7 at the center thereof. Electromagnets 19 and 20 are arranged so as to sandwich the metal disk 18 and face each other. The electromagnet 19 attracts the metal disk 18 upward by magnetic force, and the electromagnet 20 attracts the metal disk 18 downward.
The control device 70 appropriately adjusts the magnetic force exerted by the electromagnets 19 and 20 on the metal disk 18 so that the shaft 7 is magnetically levitated in the thrust direction and held in a non-contact manner in the space.

Further, a displacement sensor 17 is disposed so as to face the lower end portion of the shaft 7. The displacement sensor 17 samples and detects the displacement of the shaft 7 in the thrust direction, and transmits this to the control device 70. The control device 70 detects the displacement of the shaft 7 in the thrust direction based on the displacement detection signal received from the displacement sensor 17.
When the shaft 7 moves in one of the thrust directions and is displaced from a predetermined position, the control device 70 adjusts the magnetic force by feedback controlling the exciting currents of the electromagnets 19 and 20 so as to correct this displacement. It operates to return 7 to a predetermined position. The control device 70 performs this feedback control continuously. Thereby, the shaft 7 is magnetically levitated and held at a predetermined position in the thrust direction.
As described above, the shaft 7 is held in the radial direction by the magnetic bearings 12 and 13 and is held in the thrust direction by the magnetic bearing 14, so that the shaft 7 rotates around the axis of the shaft 7.

Next, the fixed part which comprises a gas transfer mechanism is demonstrated.
The fixed portion includes a fixed blade 30 provided on the intake port 4 side (turbo molecular pump portion T), a thread groove spacer 31 provided on the exhaust port 6 side (thread groove type pump portion S), a stator column 34, and the like. Has been.
The fixed wing 30 is composed of a blade that is inclined by a predetermined angle from a plane perpendicular to the axis of the shaft 7 and extends from the inner peripheral surface of the casing 2 toward the shaft 7.
In the turbo molecular pump section T, these fixed blades 30 are formed in a plurality of stages alternately with the rotor blades 9 in the axial direction. The fixed wings 30 at each stage are separated from each other by a cylindrical spacer 33.

The thread groove spacer 31 is a cylindrical member having a spiral groove 32 formed on the inner peripheral surface. The inner peripheral surface of the thread groove spacer 31 faces the outer peripheral surface of the cylindrical member 10 with a predetermined gap therebetween.
The direction of the spiral groove 32 formed in the thread groove spacer 31 is the direction toward the exhaust port 6 when the gas is transported in the spiral groove 32 in the rotational direction of the rotating portion. The depth of the spiral groove 32 becomes shallower as it approaches the exhaust port 6. The gas transported through the spiral groove 32 is compressed as it approaches the exhaust port 6.
The base 3 constitutes an exterior body of the turbo molecular pump 1 together with the casing 2. At the center of the base 3 in the radial direction, a stator column 34 having a cylindrical shape concentric with the rotation axis of the rotor is attached in the direction of the intake port 4.

The turbo molecular pump 1 is provided with a protective bearing (auxiliary bearing) 40 formed of a full-groove type deep groove ball bearing on the intake port 4 side of the displacement sensor 15 inside the casing 2.
The details of the protective bearing 40 will be described later.
Further, on the exhaust port 6 side of the displacement sensor 16, a protective bearing 50 configured by a pair of angular ball bearings in which oblique contact directions are combined in opposite directions is provided.
These protective bearings 40 and 50 are rolling bearings (touch-down bearings) for protecting the shaft 7 from contact with the magnetic bearings 12, 13, and 14 when the shaft 7 is stopped or abnormally controlled. ).

A gap slightly smaller than the gap between the shaft 7 and the magnetic bearings 12, 13, 14 is interposed between the outer peripheral surface of the shaft 7 and the inner peripheral surfaces of the protective bearings 40, 50.
As a result, in a state where the shaft 7 is rotatably supported by the magnetic bearings 12, 13, and 14 in a magnetically levitated state, the shaft 7 maintains a non-contact state with respect to the protective bearings 40 and 50. On the other hand, when the shaft 7 is stopped or when the control is abnormal due to the action of an external force or the like, the shaft 7 comes into contact with the protective bearings 40 and 50 and is rotatably supported before contacting the magnetic bearings 12, 13 and 14.

Here, a method of assembling (assembling) the shaft 7 in the turbo molecular pump 1 configured as described above will be briefly described.
In the turbo molecular pump 1 according to the present embodiment, the rotor body 8 is fixed to the shaft 7 using bolts 23. A permanent magnet 111 constituting the motor unit 11 (high frequency motor) is embedded in the shaft 7 in advance.

On the other hand, on the fixed portion side, a cylindrical stator column 34 is fixed to the base 3 using bolts 25.
A protective bearing 40 is fixed to the inner peripheral surface of the stator column 34 near the end on the intake port 4 side.
Then, after the shaft 7 to which the rotor body 8 is fixed is inserted (inserted) into the stator column 34 from the direction of the intake port 4, the metal disk 18 (magnetic bearing 14) is attached to the shaft 7 from the direction of the exhaust port 6 (attachment). ) Assemble the rotating part to the fixed part.

Thus, when the rotating part is assembled to the fixed part, that is, when the shaft 7 is assembled to the stator column 34, the protective bearing 40 is magnetized by the magnetic field of the permanent magnet 111 embedded in the shaft 7. That is, a magnetic field remains in the protective bearing 40.
In the present embodiment, even when the protective bearing 40 is magnetized in this way, the protective bearing 40 of the shaft 7 is caused by the action of the magnetic circuit formed by the generated residual magnetic field as in the conventional case. A magnetic induction structure (magnetic induction mechanism) that suppresses the accompanying phenomenon that rotates with rotation is provided.

Here, the magnetic induction structure that suppresses the accompanying phenomenon of the protective bearing 40 will be described.
FIG. 2A is a diagram showing a configuration of the magnetic induction structure, and FIG. 2B is an enlarged view of a region indicated by a broken line part in FIG. In FIG. 2, the description of the rotor main body 8 and the like fixed to the shaft 7 is omitted in order to avoid complicated explanation.
As shown in FIG. 2, the turbo molecular pump 1 according to the present embodiment includes an inner ring 41, an outer ring 42, a protective bearing 40 including a rolling element 43, and a magnetic derivative 44.
The inner ring 41 and the outer ring 42 constitute a raceway (circular raceway) on which the rolling elements 43 in the protective bearing 40 roll.
The inner ring 41 and the outer ring 42 are formed of a magnetic member (for example, a SUS440C member that is martensitic stainless steel, SUJ2 that is carbon steel, or the like).

The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 41 and the outer ring 42, and are formed of a ceramic material that is a nonmagnetic material.
The density of the ceramic rolling element 43 (for example, 3.20 g / cm3 in the case of Si3N4 ceramics) is much lower than the density of the bearing steel (7.85 g / cm3), and therefore the centrifugal force generated when rotating at high speed. Can be effectively suppressed, and the load on the rolling element 43 can be reduced.

The magnetic derivative 44 is a member formed of a magnetic material, and has a magnetic induction function for guiding the magnetism of the magnetized inner ring 41 to a closed magnetic path passing through the inner ring 41 and the outer ring 42, and a protective bearing 40 (outer ring 42) as a stator. And a fixing function for fixing to the column 34.
As shown in the figure, the magnetic derivative 44 includes a bearing fixing portion 44a and a magnetic induction portion 44b.

The bearing fixing portion 44a is made of an annular plate member, and has a plurality of through holes 47 into which screws 45 for fixing (wearing) the magnetic derivative 44 to the stator column 34 are fitted (pushed).
Further, a screw hole 48 for fixing the screw 45 is provided on the end surface of the stator column 34 on the intake port 4 side.
The protective bearing 40 in which the outer ring 42 is disposed in the fitting groove 46 provided at the end of the stator column 34 on the intake port 4 side is fixed to the screw hole 48 with the screw 45 so that the intake port It is pressed and fixed from the 4th side.

The magnetic induction portion 44b is configured by a portion projecting (protruding) in the extending direction (radial direction) and the axial direction of the bearing fixing portion 44a from the inner peripheral edge portion of the bearing fixing portion 44a.
A portion protruding in the axial direction (exhaust port 6 direction) in the magnetic induction portion 44b is disposed between the inner ring 41 and the outer ring 42 of the protective bearing 40, and with respect to the outer peripheral surface and the inner peripheral surface of the outer ring 42, The contact (contact) is made so that the magnetic resistance becomes smaller.
Thus, by bringing the magnetic derivative 44 and the outer ring 42 into contact, more magnetic flux can be picked up and guided to a closed magnetic path (thick line) passing through the inner ring 41 and the outer ring 42. A closed magnetic path (thick line) passing through the inner ring 41 and the outer ring 42 is an induction magnetic path.

Further, as shown in FIG. 2B, the gap β between the inner ring 41 of the protective bearing 40 and the magnetic guiding portion 44b is equal to the gap α between the inner peripheral surface of the inner ring 41 and the outer peripheral wall surface of the shaft 7. It is configured to be sufficiently small (narrow) in comparison.
In addition, the interval β is a distance between a gap between the radially projecting portion of the magnetic guide portion 44b and the end face on the inlet 4 side of the inner ring 41, and a portion of the magnetic guide portion 44b protruding in the axial direction. The distance of the space | gap between the inner peripheral wall surfaces of the inner ring | wheel 41 is shown.
Thus, by providing the magnetic derivative 44 so that the interval β <the interval α, it is possible to pick up more magnetic flux and guide it to the closed magnetic circuit (thick line) passing through the inner ring 41 and the outer ring 42.

Next, a state in which the protective bearing 40 configured in this way is magnetized by the permanent magnet 111 when the turbo molecular pump 1 is assembled (assembled) will be described.
FIG. 3 is a diagram illustrating a state in which the protective bearing 40 according to the present embodiment is magnetized.
3A shows a cross section in the radial direction (radial direction) of the protective bearing 40, and FIG. 3B shows a cross section in the axial direction (axial direction).
As described above, when the protective bearing 40 is magnetized, as shown in FIG. 3, a closed magnetic path (broken line) passing through the inner ring 41 and the shaft 7 and a closed magnetic path (thick line) passing through the inner ring 41 and the outer ring 42, that is, Two systems of magnetic circuits are formed.

In the turbo molecular pump 1 according to the present embodiment, as shown in FIG. 2, by providing a magnetic derivative 44 that guides the magnetized magnetism of the inner ring 41 to the outer ring 42, in a closed magnetic circuit passing through the inner ring 41 and the outer ring 42. The air gap interval β is smaller than the conventional air gap interval (shown in FIG. 9) (the interval between the inner ring 101 and the outer ring 103). That is, the magnetic resistivity in the closed magnetic path passing through the inner ring 41 and the outer ring 42 is reduced.
Therefore, the magnetic flux density (number of magnetic flux lines per unit area) of the closed magnetic circuit (thick line) passing through the inner ring 41 and the outer ring 42 is larger (higher) than the closed magnetic circuit (broken line) passing through the inner ring 41 and the shaft 7. .
Therefore, by providing the magnetic derivative 44, the magnetic flux leaking to the shaft 7 side can be reduced by guiding the magnetic flux to the closed magnetic path (thick line) passing through the inner ring 41 and the outer ring 42.

Thereby, since the induced current generated in the shaft 7 can be reduced, during the steady operation of the turbo molecular pump 1, that is, while the shaft 7 is supported in a non-contact manner by the magnetic bearings 12, 13, and 14,
(Rotational torque of inner ring 41 of protective bearing 40) <(friction torque of protective bearing 40)
The relationship is established. The friction torque of the protective bearing 40 includes a component of rolling friction force of the rolling element 43.
That is, since the force for braking the inner ring 41 is larger than the force for rotating the inner ring 41 of the protective bearing 40, the accompanying rotation of the inner ring 41 accompanying the rotation of the shaft 7 can be suppressed.

As described above, according to the present embodiment, by providing the magnetic induction structure that induces the magnetism of the magnetized protective bearing 40, the accompanying rotation of the protective bearing 40 during steady operation of the turbo molecular pump 1 is suppressed. Therefore, the wear rate (wear rate) of the protective bearing 40 can be reduced. Thereby, the lifetime of the protective bearing 40 can be extended.
According to this embodiment, since the accompanying rotation of the protective bearing 40 can be suppressed, noise (abnormal noise) and vibration caused by the rotation of the protective bearing 40 can be reduced.
Moreover, according to this Embodiment, since the magnetic flux which leaks to the shaft 7 side reduces, the temperature rise of the shaft 7 by Joule heat can be prevented.

Further, according to the present embodiment, as shown in FIG. 3, the inner ring 41 is formed so as to form a closed magnetic path (thick line) passing through the inner ring 41 and the outer ring 42 by inducing magnetic flux through the magnetic derivative 44. A force (torque) that brakes the rotation of the cylinder acts.
Therefore, after the touchdown state (when a disturbance is applied or when the control system is abnormal) is resolved, that is, when rotation support of the shaft 7 in a non-contact manner by the magnetic bearings 12, 13, and 14 is resumed. The rotation of the inner ring 41 can be stopped in a shorter time (more quickly).
Accordingly, the time (period) for idling the inner ring 41 can be shortened, so that the wear rate (wear speed) of the protective bearing 40 can be reduced. Thereby, the lifetime of the protective bearing 40 can be extended.

Note that an AC magnetic field is applied (acts) between the inner ring 41 and the outer ring 42 of the protective bearing 40 during touchdown (when the shaft 7 is stopped and when control is abnormal).
Therefore, the magnetic material forming the inner ring 41, the outer ring 42, and the magnetic derivative 44 constituting the protective bearing 40 has a small degree (rectangular ratio) indicating the rectangularity (rectangularity) of the hysteresis curve (BH curve). It is preferable to select.
Specifically, magnetic soft iron, 3% silicon iron, free-cutting silicon iron and the like are preferable.

The magnetic induction structure that suppresses the accompanying rotation of the protective bearing 40 described above is not limited to a structure in which the magnetic derivative 44 as shown in FIG.
The magnetic induction structure can suppress the influence on the shaft 7 of the magnetic circuit formed by the residual magnetic field generated in the magnetized inner ring 41, that is, shown by a broken line in FIG. Any structure that can reduce the magnetic flux density in a closed magnetic circuit (magnetic circuit) passing through the inner ring 41 and the shaft 7 may be used.
Next, a modified example of the magnetic induction structure that suppresses the accompanying rotation of the protective bearing 40 described above will be described.

(First modification)
FIG. 4 is a diagram showing a configuration of a first modification of the magnetic induction structure.
Here, parts having the same configuration as the turbo molecular pump 1 shown in the above-described embodiment are denoted by the same reference numerals, description thereof is omitted, and different configurations will be described.
As shown in FIG. 4, the magnetic induction structure shown in the first modification includes an inner ring 41, an outer ring 42, a protective bearing 40 including a rolling element 43, a bearing fixing member 51, and a magnetic derivative 52.
The inner ring 41 and the outer ring 42 constitute a raceway (circular raceway) on which the rolling elements 43 in the protective bearing 40 roll.
The inner ring 41 and the outer ring 42 are formed of magnetic members.
The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 41 and the outer ring 42, and are formed of a ceramic material that is a nonmagnetic material.

The bearing fixing member 51 is formed of an annular plate member, and a plurality of through holes 47 into which screws 45 for fixing (mounting) the protective bearing 40 to the stator column 34 are fitted (pressed) are formed.
Further, a screw hole 48 for fixing the screw 45 is provided on the end surface of the stator column 34 on the intake port 4 side.
In the protective bearing 40 in which the outer ring 42 is disposed in the fitting groove 46 provided at the end of the intake port 4 of the stator column 34 via the magnetic derivative 49, the bearing fixing member 51 is screwed into the screw hole 48 with the screw 45. By fixing, it is pressed and fixed from the inlet 4 side.

The magnetic derivative 52 is a member formed of a magnetic material having a magnetic induction function for guiding the magnetized magnetism of the inner ring 41 to a closed magnetic path that passes through the inner ring 41 and the outer ring 42, and protrudes in the axial direction (projects). ) Part.
The portion of the magnetic derivative 52 that protrudes in the axial direction (in the direction of the intake port 4) is disposed between the inner ring 41 and the outer ring 42 of the protective bearing 40, and more closely with respect to the outer peripheral surface and the inner peripheral surface of the outer ring 42. The contact (contact) is made so that the magnetic resistance is reduced.
Thus, by bringing the magnetic derivative 52 and the outer ring 42 into contact, more magnetic flux can be picked up and guided to the closed magnetic path passing through the inner ring 41 and the outer ring 42.

As shown in FIG. 4, the gap between the inner ring 41 and the magnetic derivative 52 of the protective bearing 40 is the same as the gap β between the inner ring 41 and the magnetic guiding portion 44b shown in FIG. It is configured to be sufficiently smaller (narrower) than the gap between the inner peripheral surface of 41 and the outer peripheral wall surface of the shaft 7.
Thus, by providing the magnetic derivative 52, more magnetic flux can be picked up and guided to the closed magnetic circuit passing through the inner ring 41 and the outer ring 42.
The magnetic circuit formed when the protective bearing 40 is magnetized is the same as the closed magnetic circuit shown in FIG.

(Second modification)
FIG. 5 is a diagram showing a configuration of a second modification of the magnetic induction structure.
Here, parts having the same configuration as the turbo molecular pump 1 shown in the above-described embodiments (including modifications) are denoted by the same reference numerals, description thereof is omitted, and different configurations will be described.
As shown in FIG. 5, the magnetic induction structure shown in the second modified example includes an inner ring 41, an outer ring 42, a protective bearing 40 including a rolling element 43, an upper magnetic derivative 53, and a lower magnetic derivative 54.
The inner ring 41 and the outer ring 42 constitute a raceway (circular raceway) on which the rolling elements 43 in the protective bearing 40 roll.
The inner ring 41 and the outer ring 42 are formed of magnetic members.
The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 41 and the outer ring 42, and are formed of a ceramic material that is a nonmagnetic material.

The upper magnetic derivative 53 is a member formed of a magnetic material, and has a magnetic induction function for guiding the magnetism of the magnetized inner ring 41 to a closed magnetic path passing through the inner ring 41 and the outer ring 42, and a protective bearing 40 (outer ring 42). And a fixing function for fixing to the stator column 34.
The upper magnetic derivative 53 is made of an annular plate member, and has a plurality of through holes 47 into which screws 45 for fixing (mounting) the protective bearing 40 to the stator column 34 are fitted (pressed).
Further, a screw hole 48 for fixing the screw 45 is provided on the end surface of the stator column 34 on the intake port 4 side.
The protective bearing 40 disposed in the fitting groove 46 provided at the end of the intake port 4 of the stator column 34 via the lower magnetic derivative 54 fixes the bearing fixing member 51 to the screw hole 48 with the screw 45. As a result, it is pressed and fixed from the inlet 4 side.

The inner peripheral edge portion of the upper magnetic derivative 53 protrudes inward (in the axial center direction) to the vicinity of the inner peripheral wall surface of the inner ring 41 when the protective bearing 40 is fixed to the stator column 34. However, the inner diameter of the upper magnetic derivative 53 is formed larger than the inner diameter of the inner ring 41 so as not to hinder the function as the protective bearing 40.
Further, a part of the surface on the exhaust port 6 side of the upper magnetic derivative 53 comes into contact (contact) with the end surface on the intake port 4 side of the outer ring 2 when the protective bearing 40 is fixed.

The lower magnetic derivative 54 is a member made of a magnetic material having a magnetic induction function for guiding the magnetized magnetism of the inner ring 41 to a closed magnetic path passing through the inner ring 41 and the outer ring 42, and is made of an annular plate member. .
The outer peripheral portion of the side surface of the intake port 4 in the lower magnetic derivative 54 is in contact (adhered) to the end surface on the exhaust port 6 side of the outer ring 2 so that the magnetic resistance becomes smaller.
Thus, by bringing the upper magnetic derivative 53 and the lower magnetic derivative 54 into contact with the outer ring 42, more magnetic flux can be picked up and guided to the closed magnetic path passing through the inner ring 41 and the outer ring 42.

Further, as shown in FIG. 5, the gap between the upper magnetic derivative 53 and the lower magnetic derivative 54 and the inner ring 41 of the protective bearing 40 is the same as the gap between the inner ring 41 and the magnetic guiding portion 44b shown in FIG. Similarly to the interval β, the interval between the inner peripheral surface of the inner ring 41 and the outer peripheral wall surface of the shaft 7 is sufficiently small (narrow).
Thus, by providing the upper magnetic derivative 53 and the lower magnetic derivative 54, more magnetic flux can be picked up and guided to the closed magnetic circuit passing through the inner ring 41 and the outer ring 42.
In the turbo molecular pump 1 having the magnetic induction structure shown in the second modified example, the closed magnetic path passing through the inner ring 41 and the outer ring 42 passes through the magnetic circuit (closed magnetic path) via the upper magnetic derivative 53 and the lower magnetic derivative 54. It is formed from a magnetic circuit (closed magnetic circuit).

(Third Modification)
FIG. 6 is a diagram showing a configuration of a third modification of the magnetic induction structure.
Here, parts having the same configuration as the turbo molecular pump 1 (including the modification) shown in the above-described embodiment are denoted by the same reference numerals, description thereof is omitted, and only different configurations will be described.
In the third modification, an example in which the magnetic induction structure is configured by the protective bearing 80 obtained by modifying the protective bearing 40 described above will be described.
As shown in FIG. 6, the magnetic induction structure shown in the third modification includes an inner ring 55, an outer ring 56, a protective bearing 80 including a rolling element 43, and a bearing fixing member 51.
The inner ring 55 and the outer ring 53 constitute a raceway (circular raceway) on which the rolling element 43 in the protective bearing 80 rolls.

The inner ring 55 and the outer ring 56 are formed of magnetic members.
The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 55 and the outer ring 56, and are formed of a ceramic material that is a non-magnetic substance.
The depth of the groove of the raceway ring on which the rolling element 43 rolls, that is, the groove into which the rolling element 43 is fitted, formed on the outer peripheral wall surface of the inner ring 55 and the inner peripheral wall surface of the outer ring 56 is the protective bearing shown in FIG. It is formed deeper than 40 (inner ring 41, outer ring 42).
As shown in FIG. 6, the gap between the opposing wall surfaces of the inner ring 55 and the outer ring 56 excluding the raceway groove region, that is, the gap between the outer peripheral wall surface of the inner ring 55 excluding the raceway groove region and the inner peripheral wall surface of the outer ring 56. 2 is compared with the gap interval α between the inner peripheral surface of the inner ring 55 and the outer peripheral wall surface of the shaft 7 in the same manner as the gap β between the inner ring 41 and the magnetic guide portion 44b shown in FIG. It is configured to be sufficiently small (narrow).

Thus, by narrowing (decreasing) the distance (gap) between the inner ring 55 and the outer ring 56 in the protective bearing 80, more magnetic flux can be picked up and guided to the closed magnetic circuit passing through the inner ring 55 and the outer ring 56. .
In the turbo molecular pump 1 having the magnetic induction structure shown in the third modified example, a magnetic circuit (closed magnetic circuit) passing through the inner ring 55 and the outer ring 56 is formed by the magnetic flux passing through the gap between the inner ring 55 and the outer ring 56. It is formed. That is, magnetic flux (lines of magnetic force) is induced to the induction magnetic path.
Further, in the third modified example, as shown in FIG. 6, by increasing the thicknesses of the inner ring 55 and the outer ring 56, the cross-sectional area of the induction magnetic path can be further increased. Thereby, since the allowable limit of magnetic flux density increases, it becomes difficult to cause magnetic saturation in the protective bearing 80.

(Fourth modification)
FIG. 7 is a view showing a configuration of a fourth modification of the magnetic induction structure.
Here, parts having the same configuration as the turbo molecular pump 1 (including the modification) shown in the above-described embodiment are denoted by the same reference numerals, description thereof is omitted, and only different configurations will be described.
In the fourth modification, an example will be described in which the magnetic induction structure is configured by a protection bearing 81 obtained by further modifying the protection bearing 80 shown in the third modification.
As shown in FIG. 7, the magnetic induction structure shown in the fourth modification includes an inner ring 57, an outer ring 58, a protective bearing 81 including a rolling element 43, and a bearing fixing member 51.

The inner ring 57 and the outer ring 58 constitute a raceway (circular raceway) on which the rolling element 43 in the protective bearing 81 rolls.
The inner ring 57 and the outer ring 58 are formed of a magnetic member.
The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 57 and the outer ring 58, and are formed of a ceramic material that is a non-magnetic material.
As in the third modification, the depth of the raceway ring on which the rolling element 43 rolls, that is, the depth of the groove into which the rolling element 43 is fitted, is formed on the outer peripheral wall surface of the inner ring 57 and the inner peripheral wall surface of the outer ring 58. It is formed deeper than the protective bearing 40 (inner ring 41, outer ring 42) shown in FIG.

Further, the outer ring 58 is provided with a magnetic induction part 59 that protrudes (projects) inward (in the axial center direction) from the end of the outer ring 58 on the intake port 4 side. The magnetic guiding portion 59 is formed integrally with the outer ring 58 by a magnetic member.
The magnetic induction unit 59 has a magnetic induction function for inducing the magnetism of the magnetized inner ring 57 to a closed magnetic path passing through the inner ring 57 and the outer ring 58.
Thus, by forming the magnetic induction portion 59 integrally with the outer ring 58, more magnetic flux can be picked up and guided to the closed magnetic circuit passing through the inner ring 57 and the outer ring 58.
The inner peripheral edge portion of the magnetic guide portion 59 projects inward (in the axial center direction) to the vicinity of the inner peripheral wall surface of the inner ring 41. However, the inner diameter of the magnetic induction portion 59 is formed larger than the inner diameter of the inner ring 57 so as not to hinder the function as the protective bearing 81.

As shown in FIG. 7, the gap between the outer peripheral wall surface of the inner ring 57 excluding the raceway groove region and the inner peripheral wall surface of the outer ring 58, and the gap between the magnetic guide portion 59 and the inner ring 57 are the same as those shown in FIG. In the same manner as the gap interval β between the inner ring 41 and the magnetic guide portion 44b, the gap interval α between the inner peripheral surface of the inner ring 57 and the outer peripheral wall surface of the shaft 7 is sufficiently small (narrow). It is configured.
As a result, more magnetic flux can be picked up and guided to the closed magnetic path passing through the inner ring 55 and the outer ring 56.
Further, in the fourth modification, by providing the magnetic induction portion 59, the cross-sectional area of the induction magnetic path can be further increased. As a result, the allowable limit of the magnetic flux density further increases, so that it is difficult to cause magnetic saturation in the protective bearing 81.

(Fifth modification)
FIG. 8 is a diagram showing a configuration of a fifth modification of the magnetic induction structure.
Here, portions having the same configuration as the turbo molecular pump 1 (including the modification) shown in the above-described embodiment are denoted by the same reference numerals, description thereof is omitted, and different configurations will be described.
In the fifth modification, an example in which a magnetic induction structure is configured by a protective bearing 82 and a magnetic derivative 63 obtained by further modifying the protective bearing 80 shown in the third modification will be described.
As shown in FIG. 8, the magnetic induction structure shown in the fifth modified example includes an inner ring 60, an outer ring 61, a protective bearing 82 including a rolling element 43, a magnetic derivative 63, and a bearing fixing member 51.

The inner ring 60 and the outer ring 61 constitute a raceway (circular raceway) on which the rolling element 43 in the protective bearing 81 rolls.
The inner ring 57 and the outer ring 58 are formed of a magnetic member.
The rolling elements 43 are balls (balls) disposed between the circular raceways of the inner ring 60 and the outer ring 61, and are formed of a ceramic material that is a nonmagnetic material.
As in the third modification, the depth of the raceway ring on which the rolling element 43 rolls, that is, the depth of the groove into which the rolling element 43 is fitted, is formed on the outer circumferential wall surface of the inner ring 60 and the inner circumferential wall surface of the outer ring 61. It is formed deeper than the protective bearing 40 (inner ring 41, outer ring 42) shown in FIG.

The outer ring 61 is provided with a magnetic guiding portion 62 that protrudes (projects) inward (in the axial center direction) from the end of the outer ring 61 on the exhaust port 6 side. The magnetic guiding portion 62 is formed integrally with the outer ring 61 by a magnetic member.
The magnetic induction unit 62 has a magnetic induction function for guiding the magnetism of the magnetized inner ring 60 to a closed magnetic path passing through the inner ring 60 and the outer ring 61.
Thus, by forming the magnetic induction portion 62 integrally with the outer ring 61, more magnetic flux can be picked up and guided to the closed magnetic path passing through the inner ring 60 and the outer ring 61.

A magnetic derivative 63 made of an annular plate member made of a magnetic material is provided on the end face of the outer ring 61 on the inlet 4 side.
The magnetic derivative 63 also has a magnetic induction function for guiding the magnetism of the magnetized inner ring 60 to a closed magnetic path passing through the inner ring 60 and the outer ring 61.
Note that the inner peripheral edge portions of the magnetic induction portion 62 and the magnetic derivative 63 project inward (in the axial center direction) to the vicinity of the inner peripheral wall surface of the inner ring 60. However, the inner diameters of the magnetic induction portion 62 and the magnetic derivative 63 are formed larger than the inner diameter of the inner ring 60 so as not to hinder the function as the protective bearing 82.

The protective bearing 82 in which the outer ring 61 is disposed in the fitting groove 46 is pressed and fixed from the inlet 4 side by fixing the bearing fixing member 51 to the screw hole 48 with the screw 45 via the magnetic derivative 63. The
By bringing the magnetic derivative 63 and the outer ring 61 into contact, more magnetic flux can be picked up and guided to a closed magnetic path passing through the inner ring 60 and the outer ring 61.

As shown in FIG. 8, the gap between the outer peripheral wall surface of the inner ring 60 and the inner peripheral wall surface of the outer ring 61 excluding the raceway groove region, and the gap between the magnetic induction portion 62 and the magnetic derivative 63 and the inner ring 60 are described above. 2 is sufficiently smaller (narrower) than the gap interval α between the inner peripheral surface of the inner ring 60 and the outer peripheral wall surface of the shaft 7 as well as the gap interval β between the inner ring 41 and the magnetic guide portion 44b shown in FIG. It is configured as follows.
As a result, more magnetic flux can be picked up and guided to the closed magnetic path passing through the inner ring 60 and the outer ring 61.
In the fifth modification, the magnetic induction section 62 and the magnetic derivative 63 are provided, so that the cross-sectional area of the induction magnetic path can be further increased. As a result, the allowable limit of the magnetic flux density further increases, so that it is difficult to cause magnetic saturation in the protective bearing 82.

It is the figure which showed schematic structure of the turbo-molecular pump which concerns on this Embodiment. (A) is the figure which showed the structure of the magnetic induction structure, (b) shows the enlarged view of the area | region shown in the broken-line part of (a). It is a figure which shows the state by which the protective bearing which concerns on this Embodiment was magnetized. It is the figure which showed the structure of the 1st modification of a magnetic induction structure. It is the figure which showed the structure of the 2nd modification of a magnetic induction structure. It is the figure which showed the structure of the 3rd modification of a magnetic induction structure. It is the figure which showed the structure of the 4th modification of a magnetic induction structure. It is the figure which showed the structure of the 5th modification of a magnetic induction structure. It is a figure which shows the state by which the bearing ring was magnetized in the conventional protective bearing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Turbo molecular pump 2 Casing 3 Base 4 Intake port 5 Flange part 6 Exhaust port 7 Shaft 8 Rotor main body 9 Rotor blade 10 Cylindrical member 11 Motor part 12-14 Magnetic bearing 15-17 Displacement sensor 18 Metal disk 19, 20 Electromagnet 23 Bolt 25 Bolt 30 Fixed blade 31 Thread groove spacer 32 Spiral groove 33 Spacer 34 Stator column 40, 50 Protective bearing 41 Inner ring 42 Outer ring 43 Rolling element 44 Magnetic derivative 70 Controller 111 Permanent magnet

Claims (7)

A bearing device that supports a rotating shaft provided with permanent magnets constituting a motor in a non-contact manner,
Comprising a rolling bearing made of a non-magnetic material and an inner ring and an outer ring made of a magnetic material that form a raceway of the rolling material, and comprising a protective bearing that supports the rotating shaft when stopped and abnormally,
The bearing device has a magnetic induction structure that makes a rotational torque of the inner ring smaller than a friction torque.   2. The bearing device according to claim 1, wherein the magnetic induction structure comprises a magnetic induction member made of a magnetic member for guiding the magnetism of the inner ring to the outer ring. The magnetic induction member is disposed with a predetermined distance β from the inner ring,
The bearing device according to claim 2, wherein the interval β is smaller than an interval α between the rotating shaft and the inner ring.   4. The bearing according to claim 1, wherein the magnetic induction structure is configured such that an interval γ between the inner ring and the outer ring is smaller than an interval α between the rotating shaft and the inner ring. apparatus.   The bearing device according to claim 1, wherein the rolling element is made of a ceramic member.   The bearing device according to claim 1, wherein the rotating shaft is supported by magnetic force or dynamic pressure.   A turbo-molecular pump comprising the bearing device according to any one of claims 1 to 6.

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