JPH0240096A - Operation control method for turbo-molecular pump - Google Patents

Abstract

PURPOSE:To abate any possibility of accident happening at the time of passing a resonance point by floating a rotor up to a balancing point with an axial magnetic bearing in place of a mechanical bearing, after the rotating rotor has passed through the primary resonance point. CONSTITUTION:A rotor shaft 4 is a little more lowered than a proper floating position, and in the state that a flange part 31 of this rotor shaft 4 is made lightly contact with a rolling bearing 12, rotation and drive of a rotor blade 5 is started. When rotating speed of this rotor blade 5 is reached to the specified one after passing through a primary resonance point of an upper magnetic bearing 8 and that of a lower magnetic bearing 9, a control current to a control coil 29 is gradually increased and thereby the rotor shaft is floated by degrees. This actuation should be done till the rotor shaft 4 is reached a balancing point, simultaneously the rotor blade 5 is reached to the specified rating speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the operation of a turbomolecular pump.

In turbomolecular pumps, active magnetic bearings are generally used in both the radial and axial directions of the rotor, but from the viewpoint of easier control and cost reduction, It is preferable to use a uniaxially controlled magnetic bearing device in which an active magnetic bearing is used only in the rotation axis direction and a passive magnetic bearing is used in the radial direction. However, radial passive magnetic bearings do not have good damping characteristics, so the amplitude multiplier at the resonance point is large, and in order to prevent accidents when passing through the resonance point,
There is a need to implement various measures.

The present invention has been made in view of the above, and an object thereof is to provide an operation control method for a turbomolecular pump that can reduce the possibility of an accident occurring when passing through a resonance point.

Therefore, the turbo molecular pump operation control method of this invention is as follows:
Inside the casing, the rotor is radially supported by a radial magnetic bearing, and supported by an axial magnetic bearing so that its axial floating position can be adjusted. A mechanical bearing was provided to support the rotor in the axial direction, and the rotor was supported by the mechanical bearing until the rotation speed of the rotor passed through the primary resonance point, and the rotation speed of the rotor passed through the primary resonance point. Later, the rotor is levitated to an equilibrium point using the axial magnetic bearing.

Next, specific embodiments of the turbo molecular pump operation control method of the present invention will be described in detail with reference to the drawings.

In FIG. 1, ■ indicates the entire turbo molecular pump, and this pump 1 rotates a rotor shaft 4 by a motor 3 disposed inside a main body casing 2, thereby rotating a turbo blade 5. It has a structure in which the intake air from the intake port 6 is exhausted from the exhaust port. The rotor shaft 4 has passive magnetic bearings 8.
9 provides radial support, and an active magnetic bearing 10 provided at the bottom provides axial support.

In the figure, reference numeral 12 denotes rolling bearings, and these are mainly for safety purposes to restrict the maximum displacement of the rotor shaft 4, but the upper rolling bearing 12 also has other important functions. This point will be discussed later.

The lower magnetic bearing 9 is composed of a pair of permanent magnets 13, 13, which are arranged so that the same poles are located at opposite positions. The lower magnetic bearing 9 also has a free rocking body 15 that is swingably disposed at the bottom of the main body casing 2, and the free rocking body 15 and the rotor shaft 4 are magnetically connected to each other by permanent magnets 16 and 16. is combined with The raised position of the free rocking body 15 is
The ball 17 prevents contact with the rotor shaft 4, and a damping material 18 such as a magnetic fluid is interposed between the free-swinging body 15 and the main casing 2. That is, in this lower magnetic bearing 9, sufficient damping ability can be imparted to the rotor shaft 4 by the free rocking body 15 and the damping material 18.

On the other hand, in the upper magnetic bearing 8, a free rocking body 19 is swingably supported at the top of the main body casing 2, and a pair of permanent magnets 20, 20 are interposed between the free rocking body 19 and the rotor shaft 4. A magnetic bearing is configured.

The free rocking body 19 is magnetically coupled to the main body casing 2 by a pair of permanent magnets 21.21, and a damping material 22 such as a magnetic fluid is provided between the free rocking body 19 and the main body casing 2. Intervention is provided. That is, in this upper magnetic bearing 8, the free rotating body 19 and the damping material 22 are capable of imparting a damping ability to the rotor shaft 4.

Next, the active magnetic bearing 10 for providing the above-mentioned axial support
I will explain about it. In FIG. 1, 23 is an armature disk, and this armature disk 23 is attached to the rotor shaft 4 so as to be rotatable therewith. A pair of bearing elements 24, 24 are arranged on both sides of the armature disk 23 in the axial direction.

Each bearing element 24 has a structure in which a pair of magnetic pole pieces 27 and 28 are attached to both magnetic pole faces of a permanent magnet 250. At a position between the pair of magnetic pole pieces 27 and 28, a control coil 29 is disposed closer to the tip than the permanent magnet 25, and a sensor coil 30 is disposed further to the tip side of the control coil 29. It is assumed that the sensor coil 30 is wound in the same direction as the control coil 29.

In this magnetic bearing 10, a pair of sensor coils 3
At 0.30, the displacement of the armature disk 23 is differentially detected, and based on this detection result, the control coil 29.29
The rotor shaft 4 has a function of adjusting the control current to the rotor shaft 4 and thereby holding the rotor shaft 4 at an appropriate floating position. In addition, in the case of this magnetic bearing 10, the permanent magnet 25
By increasing the distance between the NS and S poles of the comb, the internal magnetic resistance can be increased (
For example, if the magnetic pole pieces 27 and 28 are made of a soft magnetic material, the magnetic resistance of the magnetic path of the control coil 29 is
By creating a leakage magnetic path and arranging the control coil 29 on the tip side of the permanent magnet 25, the control characteristics by the control current can be improved, and the unbalanced spring caused by the displacement of the armature disk 23 can be improved. This has the advantage that the constant can be made small and the configuration can be simplified.

FIG. 2 shows the relationship between the upper rolling bearing 12 and the rotor shaft 4. As shown in the figure, the rotor shaft 4 has an outer diameter that is slightly smaller than the inner diameter of the rolling bearing 12.
The upper portion thereof has a flange portion 31 having a diameter larger than the inner diameter of the rolling bearing 12. That is, the rotor shaft 4
When the roller bearing 12 is floating in the proper position, the rolling bearing 12
A predetermined gap is formed between the rotor shaft 4 and the flange portion 31, and the flange portion 31 can come into contact with the inner race of the rolling bearing 12 when the rotor shaft 4 is lowered by a predetermined amount. te 0ru.

Note that 32 is a spring, and this spring 32 is used to reduce the shock when the flange portion 31 comes into contact with and separates from the rolling bearing 12.

Next, a method of controlling the operation of the turbo molecular pump at startup will be explained based on FIG. 3. In the first stage, the rotor shaft 4 is lowered slightly below the proper floating position, and the flange portion 31 of the rotor shaft 4 is in slight contact with the rolling bearing 12, and the rotational drive of the rotor blades 5 is started. Figure 3, point A). When the rotational speed of the rotor blade 5 passes through the primary resonance point B of the upper magnetic bearing 8 and the primary resonance point C of the lower magnetic bearing 9 and reaches a predetermined rotational speed (the same point), the control coil The control current to 29 is gradually increased to levitate the rotor shaft 4 little by little. This operation is continued until the rotor blades 5 reach a predetermined rotational speed and the rotor shaft 4 reaches the equilibrium point (point E in the figure). After that, the rotor shaft 4 is floated to the equilibrium point. It performs rotational drive.

Note that, contrary to the above example, it goes without saying that it is possible to raise the floating position of the rotor above the proper floating position and obtain the same effect by devising the position of the rolling bearing 12, etc.

As described above, in the turbo molecular pump operation control method of the present invention, the rotor is supported by mechanical bearings until the rotational speed of the rotor passes through the primary resonance point. It becomes possible to reduce the risk of accidents occurring during passage, and improve the operational reliability of the pump.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of a turbomolecular pump for carrying out the operation control method of the present invention, FIG. 2 is a longitudinal sectional view showing an enlarged part of the pump, and FIG. It is an explanatory diagram of an example. ■...Turbo molecular pump, 2...Main casing,
4... Rotor shirt 1-15... Rotor blade, 8.9
...Magnetic bearing, 10...Axial magnetic bearing, 12...
・Rolling bearing. Patent applicant Nippon Ferro Fluidics Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1. While the rotor is radially supported within the casing by a radial magnetic bearing and the axial floating position is adjustable by an axial magnetic bearing, the rotor falls or rises above the axial equilibrium point. A mechanical bearing is provided to support the rotor in the axial direction at the position, and the rotor is supported by the mechanical bearing until the rotation speed of the rotor passes the primary resonance point. A method for controlling the operation of a turbo-molecular pump, characterized in that the rotor is levitated to an equilibrium point by the axial magnetic bearing after the rotor has passed.