JPH07238897A - Turbo-molecular pump - Google Patents

Abstract

PURPOSE:To solve the influence of temperature and length of a cable so that stable axial magnetic buoyancy control may be always carried out by arranging a plurality of position detecting sensors in a shaft end part area in such a way that their relative positions are different to each other so that their outputs show different characteristic to each other. CONSTITUTION:A rotor shaft 3 in a turbo-molecular pump is axially buoyantiy pivoted by thrust magnetic bearings 7, 7' which are provided to the top and bottom of a disc 8 fixed to the rotor shaft 3 so as to sandwich the disc 8, and varies magnetic buoyancy by the current change of magnetic coils 7a, 7'a. In this case, a first axial displacement detecting sensor 10a and a second axial displacement detecting sensor 10b are respectively provided to a position having space a in parallel against the opposite rotor side end surface 3' of the rotor shaft 3 and a position having space against an end surface 3'' inclined 45 deg. from a shaft center. Each output signal is transmitted to a control output treating part 12, and the axial magnetic buoyancy of the rotor shaft 3 is controlled in response to the detected displacement quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbo molecular pump used for exhausting a gas to obtain a high vacuum in a particle accelerator, a nuclear fusion device, a surface analysis device, a semiconductor manufacturing device, etc. The present invention relates to a high-speed rotary turbo molecular pump that uses a bearing.

[0002]

2. Description of the Related Art A magnetic bearing type turbo molecular pump (hereinafter referred to as T
(Abbreviated as MP) is used for obtaining an oil-free vacuum state, and a rotor shaft to which a rotor rotating at high speed is fixed is supported by magnetic buoyancy of a magnetic bearing device.

An example of a conventional TMP is shown in FIG. Reference numeral 1 denotes a rotor having a main blade for vacuum exhaustion, which is fixed to a rotor shaft 3 and is rotated at a high speed by a motor 4. Reference numeral 2 denotes a casing that surrounds the rotor. Rotor blades (moving blades) protruding from the outer circumference of the rotor 1 and stator blades (static blades) protruding from the inner circumference of the casing are alternately arranged. The evacuation action is performed. The rotor shaft 3 is supported in the radial direction by two radial magnetic bearings 5 and 6 arranged around the shaft. On the other hand, with respect to the axial direction, a levitation shaft is axially supported by thrust magnetic bearings 7 and 7'provided above and below the disk 8 fixed to the shaft 3. The radial deviation of the rotor shaft 3 is detected by the radial deviation detection sensor 9, and the output is fed back to the electromagnetic coils of the radial magnetic bearings 5 and 6 to control the magnetic buoyancy in the radial direction. The axial displacement is detected by the axial displacement detection sensor 10
Detected by the thrust magnetic bearings 7, 7 '
To control the magnetic buoyancy in the axial direction.

When the TMP is stopped, the rotor shaft 3 is directly supported by a touch bearing (not shown),
Contact with the radial magnetic bearings 5, 6 and the thrust magnetic bearings 7, 7'is prevented. In the above configuration, especially in the control of the axial displacement, the width of the displacement may be relatively large compared to the width of the radial deviation, and the axial clearance is always constant under all environmental conditions. It is difficult to control.

FIG. 6 shows the relationship between the axial displacement and the control output to the thrust magnetic bearing based on the output of the axial displacement detection sensor 10, that is, the magnetic control characteristic. Graphs of the solid line and the dotted line in the figure are shown. Indicates a state in which the magnetic control characteristics are shifted due to the influence of the temperature of the sensor itself or the circuit conditions of the control circuit, such as fluctuations in temperature and cable length. In this way, if the control characteristics shift due to changes in the environment such as temperature and cable length, the axial position control of the shaft will be disturbed, and in some cases, it may lead to an accident such as contact with the touch bearing. There is such a problem.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems, and it is always stable even when the axial control characteristics are changed by the pump operating conditions due to the influence of environmental conditions such as temperature. The present invention provides a turbo molecular pump capable of performing precise magnetic levitation control.

[0007]

In order to achieve such an object, the present invention provides two axial position detection sensors arranged in different positions in the rotor shaft end region, and uses the composite output of the two axial position detection sensors. The levitation control in the direction is performed.

[0008]

The magnetic bearing is controlled even if the conditions of the control circuit change depending on the environment by controlling so that the difference between the outputs of the two position detection sensors arranged with different relations in the shaft end region becomes zero. Feedback control can always be performed in a stable state.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. The rotor shaft 3 is axially levitationally supported by thrust magnetic bearings 7 and 7'provided above and below a disc 8 fixed thereto. The gap between the thrust magnetic bearing and the disk 8 is about 0.30 mm on each side. The magnetic buoyancy with respect to the rotor shaft 3 can be varied by energizing the electromagnetic coils 7a and 7'a held by thrust magnetic bearings oppositely sandwiching the disk 8 and changing the current.

A first axial displacement detection sensor 10a is provided at a position parallel to the end face 3'on the side opposite the rotor of the rotor shaft 3 with a gap "a" between the end face 3 "and the end face 3" inclined 45 degrees from the axis. Second axial displacement detection sensors 10b are provided at positions separated by the gap a. Sensors 10a and 10b.
Have the same characteristics, and an eddy current type sensor is used, and is mounted on a holder 14 fixed to the lower end of the thrust magnetic bearing 7 '. And each sensor 10a, 10b is
While detecting the axial displacement of the rotor shaft 3,
The output signal is transmitted to the control output processing unit 12, and is fed back to the electromagnetic coil power supply 13 of the thrust magnetic bearings 7 and 7'built in the power supply unit (not shown) of the TMP,
The magnetic buoyancy in the axial direction is controlled according to the detected displacement amount to control the magnetic buoyancy in the axial direction of the rotor shaft 3. When the rotor shaft 3 is displaced in the axial direction, one of the relations of the control characteristic output with respect to the axial displacement of each of the sensors 10a and 10b is arranged with an inclination, so that FIG.
become that way. Since the two control characteristic output graphs have different slopes and the intersecting point is the displacement a, the sensor 10a,
If the difference in the control characteristic output of 10b is controlled to be 0, the rotor shaft 3 can always be held at the position of the gap a. Even if the sensors 10a and 10b have inclinations other than 45 degrees, the graphs of the two control characteristic outputs have different inclinations, so that the intersecting points can be secured. Further, as shown in FIG. 2, the axial displacement detection sensors 10a and 10c having different characteristics are provided.
Is arranged in parallel with the axial end surface of the rotor shaft 3 at different distances, the sensor 10a is installed at the position where the rotor shaft 3 is desired to be held at the position of the shaft end and the clearance a, and the output values of the sensors 10a and 10c are set. If the sensor 10c is arranged with a step difference of δ so that the same becomes, the difference between both outputs can be controlled to be zero. In this case, the relationship of the output with respect to the displacement of the gap between the sensors 10a and 10c is as shown in FIG. Therefore, even if the sensor control characteristic output changes as shown in FIG. 6 due to the influence of temperature or the like or the variation of the cable length, the control is performed so that the difference between the two sensor control characteristic outputs becomes 0, and thus the stability is always stable. The buoyant force can be controlled, and the rotor shaft 3 does not come into contact with the touch bearing 11.

[0011]

As described above, according to the present invention, since the temperature and the cable length are not affected, the stable magnetic buoyancy control in the axial direction is achieved even if the control characteristic of the axial displacement changes depending on the operating condition of the pump. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an axial position control unit of a turbo molecular pump according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an axial displacement detecting portion according to another embodiment of the present invention.

FIG. 3 is a diagram showing characteristics of an axial position control output of the embodiment (FIG. 1) of the present invention.

FIG. 4 is a diagram showing characteristics of an axial position control output of the embodiment (FIG. 2) of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional turbo molecular pump.

FIG. 6 is a diagram showing characteristics of an axial position control output of a conventional turbo molecular pump.

[Explanation of symbols]

1 ... Rotor 2 ... Casing 3 ... Rotor shaft 4 ... Motor 5, 6 ... Radial magnetic bearing 7, 7 '... Thrust magnetic bearing 8 ... Disc 9 ... Radial direction deviation detection sensor 10 ... Axial displacement detection sensor 11 ... Touch Bearing 12 ... Control output processing unit 13 ... Electromagnetic coil power supply

Claims (1)

[Claims] 1. A rotor shaft is supported by a magnetic bearing device, and the axial displacement of the shaft is detected by a position detection sensor installed at the shaft end portion of the shaft, and the output is returned to the control unit of the magnetic bearing. In a device for holding the position of the above-mentioned position within a predetermined range, a plurality of the position detection sensors are arranged with different relative positions in the shaft end region so that the outputs have different characteristics. Molecular pump.