Pumps – Motor driven – Motor within rotary pumping member
Reexamination Certificate
2000-12-19
2003-06-10
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Motor within rotary pumping member
C417S363000, C417S423400, C417S423140, C417S423150
Reexamination Certificate
active
06575713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pump that is communicated with an external container to suck gas contained within the external container, and more particularly, to a vacuum pump that can suppress the propagation of vibrations to the external container without the use of dampers.
2. Description of the Related Art
A vacuum pump, such as a turbo-molecular pump or a thread groove-type pump, is known, which is communicated with an external container to suck gas contained within the external container. The vacuum pump is widely used to conduct a vacuum process in which a processing gas within a chamber is exhausted during dry etching, CVD or the like, with a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus or the like. The vacuum pump is also used in a measuring apparatus for an electronic microscope or the like.
The vacuum pump is constructed such that an outer cylindrical portion to be communicated with the external container is fixed at one end thereof to a base so that the gas within the external container is introduced into the interior of the outer cylindrical portion at the one end thereof. In the interior of the outer cylindrical portion, a rotor portion and a stator portion are disposed, which are connected directly to or connected through other components to the base. The outer circumferential surface of one of the rotor portion and the stator portion are confronted with the inner circumferential surface of the other to define a gas transferring section for transferring the gas between the rotor portion and the stator portion.
By the rotation of the rotor portion, the gas within the gas transferring section is transferred, and the gas within the external container is sucked therein.
In case of a turbo-molecular pump, a plurality of spacers are disposed on the stator portion coaxially to the rotor portion, and stator blades are respectively disposed between the adjacent spacers to project toward the rotor portion. Rotor blades are disposed on the rotor portion to respectively project into spacers between the adjacent stator blades. The rotor blades, when rotated, collide against and thus transport the gas molecular.
In case of a thread groove-type pump, a thread groove is formed on one of the confronted circumferential surfaces of the rotor portion and the stator portion. Thus, when the rotor is rotated, the gas is transferred using the gas viscosity.
The vacuum pump described above is applied, for instance, to an electronic microscope or other apparatuses, that are largely affected by minute vibrations.
In a related art, the vacuum pump is formed of material which can easily propagates vibrations therethrough, that is, the rotor portion and the base are formed of aluminum alloy (the logarithmic attenuation ratio thereof with respect to vibrations is about 0.0002), and the outer cylindrical portion and bolts for connecting components together are formed of SUS alloy (the logarithmic attenuation ratio thereof with respect to vibrations is about 0.01). Consequently, the vibrations associated with the rotation of the rotor portion are propagated through the stator portion and the outer cylindrical portion to adversely affect the external apparatus connected thereto.
For this reason, as shown in
FIG. 4
, a technical solution has been proposed, in which a damper D is interposed between a pipe C of the external container and the outer cylindrical portion
116
of the vacuum pump
100
to prevent vibration caused due to the rotation of the rotor portion or the like from being propagated to the external container connected to the vacuum pump.
As an example of the damper D, a thin, SUS-made cylindrical member whose circumferential surface is bent into a bellows shape, and which is coated with a silicon rubber or the like is used. This damper D is designed such that the natural frequency of the entire damper D system is 20 Hz or less in order to have the excellent damping property. During the use of the vacuum pump
100
, the damper D is tightened with a hose band or the like externally mounted to the damper D.
However, the use of the damper D as a solution of avoiding the propagation of the vibrations of the vacuum pump
100
requires an extra space in the axial direction corresponding to the length of the damper D. The space required for mounting the damper D to the vacuum pump
100
is generally about 10 cm in the axial direction. The increased cost corresponding to the damper D is also required.
The mounting and removable of the damper D requires labor and is troublesome. The property of the damper D may be changed depending on the mounting state of the damper D.
Additionally, the bellows-shaped member described above can not be formed of a high-rigidity member or a thick member because the bellows-shaped member is required to exhibit an excellent vibration suppressing effect. For this reason, if the excessive force due to the rotational torque of the rotor portion acts on the member, the member may be broken. It is conceivable to arrange a reinforcing member such as a rotation preventive member in order to eliminate the breakage, but the arrangement of the reinforcing member requires an extra cost and makes the structure of the apparatus complicated. Consequently, the maintenance work such as the mounting and removal becomes troublesome.
Further, the natural frequency of the entire pump is about 10 Hz, which is close to the natural frequency of the precession of the rotor (several Hz) generated in the case where the rotor portion of the vacuum pump is supported by magnetic bearings. Consequently, the rotational shift of the rotor portion is likely to be increased due to an external force such as an earthquake, and in some cases, the protection function is activated to stop the rotor portion.
As described above, the related vacuum pump requires the damper to be mounted to the connecting portion to the external container in order to prevent the propagation of the vibrations to the external container, but the mounting of the damper increases the cost and labor and requires the extra space, resulting in the lowering of handling ability.
Further, the related vacuum pump as described above has a built-in motor, and further a certain type of the vacuum pump uses magnetic bearings as bearings. For this reason, magnetic fluxes caused by magnets of the motor and magnetic bearings may leak externally to adversely affect the connected external container such as a vacuum apparatus.
Furthermore, the related vacuum pump as described above is designed such that the outer cylindrical member to be fixed to the vacuum apparatus is electrically connected to cores of electromagnets of the motor and magnetic bearings. In the case where a switching amplifier is used as a driving amplifier for the electromagnets of each of the motor and magnetic bearings, if the voltage applied to the coil of the electromagnet by the switching amplifier is varied, the current excited in the core of the electromagnet may be transmitted through the outer cylindrical member to the external vacuum apparatus, causing an electric noise to adversely affect the vacuum apparatus.
As described above, the related vacuum pump suffers from the generated vibrations, leakage of magnetic flux, and electric noise, which lowers performance, reliability and service life of the vacuum apparatus connected to the vacuum pump.
As a technical solution for eliminating the leakage of magnetic flux to the apparatus connected to the vacuum pump, a technique is known in which the exterior of the outer cylindrical member is housed by a shielding member formed of high permeability material, such as a silicon steel plate, for shielding the magnets of the motor and magnetic bearing. However, this technical solution has a problem in that the vacuum pump is made large in size due to the provision of the shielding member in order to obtain the sufficient shielding effect. It is conceivable to arrange a shielding member just around the exterior of the motor or
Namiki Hirotaka
Ohtachi Yoshinobu
Yamauchi Akira
Adams & Wilks
Gray Michael K.
Seiko Instruments Inc.
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