JP2688624B2 - Operation control method of turbo molecular pump - Google Patents

Description

The present invention relates to an operation control method for a turbo molecular pump.

In a turbo molecular pump, it is common to use active magnetic bearings not only in the radial direction of the rotor but also in the axial direction, but from the viewpoints of easy control, cost reduction, etc. It is preferable to use a uniaxial control type magnetic bearing device in which the active magnetic bearing is used only in the rotation axis direction and the passive magnetic bearing is used in the radial direction. However, the passive magnetic bearing in the radial direction does not have a good damping characteristic, so that the amplitude magnification at the resonance point is large, and it is necessary to take various measures to prevent an accident when passing through the resonance point.

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

Therefore, according to the operation control method of the turbo molecular pump of the present invention, the rotor is supported by the radial magnetic bearings in the casing in the radial direction, and the axial levitation position is adjustable by the magnetic bearings. Is provided with a mechanical bearing that axially supports the rotor at a position lower or higher than the axial equilibrium point, and the rotor is supported by the mechanical bearing until the rotational speed of the rotor passes the primary resonance point. After the rotational speed of the rotor has passed the primary resonance point, the rotor is levitated to the equilibrium point by the axial magnetic bearing.

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

In FIG. 1, reference numeral 1 denotes the entire turbo molecular pump, but this pump 1 drives a rotor shaft 4 to rotate by a motor 3 arranged in a main body casing 2,
As a result, the turbo blade 5 is rotated and the intake air from the intake port 6 is exhausted from the exhaust port. The rotor shaft 4 is radially supported by the passive magnetic bearings 8 and 9 at both upper and lower portions thereof, and is axially supported by the active magnetic bearing 10 provided at the lower portion. In the figure, 12 are rolling bearings, which are mainly for safety that regulate the maximum displacement amount of the rotor shaft 4, but the upper rolling bearing 12 also has other important functions. This point will be described later.

The lower magnetic bearing 9 is composed of a pair of permanent magnets 13 and 13, and these are arranged so that the same poles exist at positions facing each other. Further, the lower magnetic bearing 9 is a free rocking body that is rockably arranged on the bottom of the main body casing 2.
15 has the free rocker 15 and the rotor shaft 4.
And are magnetically coupled by the permanent magnets 16, 16. The raised position of the free oscillating body 15 is regulated by a ball 17 so as not to contact the rotor shaft 4, and a damping material 18 such as a magnetic fluid is provided between the free oscillating body 15 and the main body casing 2. Is installed. That is, in the lower magnetic bearing 9, the free oscillating body 15 and the damping material 18 can impart sufficient damping ability to the rotor shaft 4.

On the other hand, in the upper magnetic bearing 8, the main body casing 2
A free oscillating body 19 is swingably supported on the top of the rotor, and a pair of permanent magnets is provided between the free oscillating body 19 and the rotor shaft 4.
20 and 20 are provided to form a magnetic bearing. The free oscillating body 19 includes a main body casing 2, a pair of permanent magnets 21,
This free rocker is magnetically coupled by 21
A damping material such as magnetic fluid is provided between the body 19 and the main casing 2.
22 are installed. That is, in the upper magnetic bearing 8, the free rotating body 19 and the damping material 22 can impart damping capability to the rotor shaft 4.

Next, the active magnetic bearing 10 for performing the above axial support is provided.
Will be described. In FIG. 1, reference numeral 23 is an armature disc, and the armature disc 23 is attached to the rotor shaft 4 so as to be integrally rotatable. A pair of bearing elements 24, 24 are arranged at positions on both sides in the axial direction with the armature disc 23 interposed therebetween. Each bearing element 24 has a structure in which a pair of magnetic pole pieces 27 and 28 are attached to both magnetic pole surfaces of a permanent magnet 25. A control coil 29 is arranged on the tip side of the permanent magnet 25 at a position between the pair of magnetic pole pieces 27, 28.
The sensor coil 30 is arranged further on the tip side than 29. The sensor coil 30 is the control coil 29 described above.
Shall be wound in the same direction as. In this magnetic bearing 10, the displacement of the armature disk 23 is differentially detected by the pair of sensor coils 30 and 30, and the control current to the control coils 29 and 29 is adjusted based on the detection result. It has a function of holding the rotor shaft 4 at an appropriate floating position. Further, in the case of this magnetic bearing 10, the NS pole face spacing of the permanent magnet 25 is increased to increase the internal magnetic resistance (for example, the magnetic pole pieces 27 and 28 are made of a soft magnetic material), and the control coil 29 is The magnetic path and its magnetic resistance are optimized by creating a leakage magnetic path of the permanent magnet 25, and by disposing the control coil 29 on the tip side of the permanent magnet 25, the control characteristics by the control current can be improved, and
This has the advantage that the unbalanced spring constant due to the displacement of the armature disk 23 can be reduced 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 same figure, the rotor shaft 4 has an outer diameter slightly smaller than the inner diameter of the rolling bearing 12, The rolling bearing 12 has a flange portion 31 having a diameter larger than the inner diameter of the rolling bearing 12. That is, while the rotor shaft 4 is floating at the proper position, a predetermined gap L is formed between the rolling bearing 12 and the flange portion 31, while when the rotor shaft 4 descends by a predetermined amount or more, The flange portion 31 is adapted to come into contact with the inner race of the rolling bearing 12. 32 is a spring, and this spring
Reference numeral 32 is for reducing a shock when the flange portion 31 comes into contact with and separates from the rolling bearing 12.

Next, an operation control method at the time of starting the turbo molecular pump will be described with reference to FIG. In the first stage, the rotor shaft 4 is slightly lowered from the proper floating position, and the rotary drive of the rotor blades 5 is started in a state where the flange portion 31 of the rotor shaft 4 is in slight contact with the rolling bearing 12 ( (Point A in Figure 3). When the rotation 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 rotation speed (point D in the figure), control is performed. The control current to the coil 29 is gradually increased to gradually float the rotor shaft 4.
This operation is performed when the rotor blade 5 reaches a predetermined rotation speed,
This is performed until the rotor shaft 4 reaches the equilibrium point (see FIG.
Point) and thereafter, the rotational drive is performed in a state where the rotor shaft 4 is levitated at the equilibrium point.

It is needless to say that contrary to the above example, it is possible to raise the rotor levitation position above the proper levitation position to obtain the same effect by devising the position of the rolling bearing 12 and the like.

As described above, in the operation control method for the turbo molecular pump of the present invention, the rotor is supported by the mechanical bearing until the rotation speed of the rotor passes through the primary resonance point. It is possible to reduce the risk of an accident occurring when passing, and improve the operational reliability of the pump.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a turbo molecular pump for carrying out the operation control method of the present invention, FIG. 2 is a longitudinal sectional view showing a part of the turbo molecular pump in an enlarged manner, and FIG. It is an explanatory view of an example. 1 ... Turbo molecular pump, 2 ... Main body casing, 4 ...
... Rotor shaft, 5 ... Rotor blade, 8,9 ... Magnetic bearing, 10 ... Axial magnetic bearing, 12 ... Rolling bearing.

Claims (1)

(57) [Claims] Claim: What is claimed is: 1. In a casing, a rotor is supported by radial magnetic bearings in a radial direction, and an axial magnetic bearing is adjustably supported in an axial flying position, while the rotor is lower than an axial equilibrium point. Alternatively, a mechanical bearing for axially supporting the rotor at an elevated position is provided, the rotor is supported by the mechanical bearing until the rotational speed of the rotor passes a primary resonance point, and the rotational speed of the rotor is primary. A method of controlling operation of a turbo molecular pump, characterized in that the rotor is levitated to the equilibrium point by the axial magnetic bearing after passing through the resonance point.