Pumps – Successive stages
Reexamination Certificate
1999-03-24
2001-01-30
Walberg, Teresa (Department: 3742)
Pumps
Successive stages
C415S090000
Reexamination Certificate
active
06179573
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to high vacuum pumps used for evacuating an enclosed vacuum chamber and, more particularly, to compact vacuum pump structures. The invention relates to vacuum pumps of the type which incorporate an electrical motor, such as for example turbomolecular pumps, molecular drag pumps and hybrid pumps.
BACKGROUND OF THE INVENTION
Conventional turbomolecular vacuum pumps include a housing having an inlet port, an interior chamber containing a plurality of axial pumping stages and an exhaust port. The exhaust port is typically attached to a roughing vacuum pump. Each axial pumping stage includes a stator having inclined blades and a rotor having inclined blades. The rotor and stator blades are inclined in opposite directions. The rotor blades are rotated at high speed by a motor to pump gas between the inlet port and the exhaust port. A typical turbomolecular vacuum pump may include nine to twelve axial pumping stages.
Variations of the conventional turbomolecular vacuum pump are known in the art. In one prior art configuration, one or more of the axial pumping stages are replaced with disks which rotate at high speed and function as molecular drag stages. This configuration is disclosed in U.S. Pat. No. 5,238,362 issued Aug. 24, 1993 to Casaro et al. A turbomolecular vacuum pump including an axial turbomolecular compressor and a molecular drag compressor in a common housing is sold by Varian Associates, Inc. under Model No. 969-9007. Turbomolecular vacuum pumps utilizing molecular drag disks and regenerative impellers are disclosed in German Patent No. 3,919,529 published Jan. 18, 1990.
Molecular drag compressors include a rotating disk and a stator. The stator defines a tangential flow channel and an inlet and an outlet for the tangential flow channel. A stationary baffle, often called a stripper, disposed in the tangential flow channel separates the inlet and the outlet. As is known in the art, the momentum of the rotating disk is transferred to gas molecules within the tangential flow channel, thereby directing the molecules toward the outlet.
Another type of molecular drag compressor includes a cylindrical drum that rotates within a housing having a cylindrical interior wall in close proximity to the rotating drum. The outer surface of the cylindrical drum is provided with a helical groove. As the drum rotates, gas is pumped through the groove by molecular drag.
A prior art high vacuum pump is shown in
FIG. 4. A
housing
10
defines an interior chamber
12
having an inlet port
14
and an exhaust port
16
. The housing
10
includes a vacuum flange
18
for sealing the inlet port to a vacuum chamber (not shown) to be evacuated. The exhaust port
16
is typically connected to a roughing vacuum pump (not shown). In cases where the vacuum pump is capable of exhausting to atmospheric pressure, the roughing pump is not required. Located within housing
10
is an axial turbomolecular compressor
20
, which typically includes several axial turbomolecular stages, and a molecular drag compressor
22
, which typically includes several molecular drag stages. Each stage of the axial turbomolecular compressor
20
includes a rotor
24
and a stator
26
. Each rotor and stator has inclined blades as is known in the art. Each stage of the molecular drag compressor
22
includes a rotor disk
30
and a stator
32
. The rotor
24
of each turbomolecular stage and the rotor
30
of each molecular drag stage are attached to a drive shaft
34
. The drive shaft
34
is rotated at high speed by a motor located in a motor housing
38
.
Turbomolecular vacuum pumps and related types of vacuum pumps are used in a wide variety of applications. In many applications, the physical size of the vacuum pump is an important system design consideration. For example, vacuum pumps are frequently used in semiconductor processing equipment that is located in or adjacent to clean room facilities. In such applications, strict limitations are placed on the size of the equipment. Another application requiring small size is portable instruments. Referring again to
FIG. 4
, it may be observed that the motor housing
38
accounts for a significant fraction of the overall length of the vacuum pump.
Accordingly, there is a need for vacuum pump structures which are compact and which are simple to manufacture.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a vacuum pump is provided. The vacuum pump comprises a housing having an inlet port and an exhaust port, a motor disposed in the housing, and one or more vacuum pumping stages disposed in the housing and operationally coupled to the motor for pumping gas from the inlet port to the exhaust port. The motor has an inverted configuration wherein a stator is disposed on a central axis and a rotor is disposed around the stator. The rotor rotates about the central axis when the motor is energized.
At least part of the motor may be located in a central portion of the vacuum pumping stages, so that the vacuum pumping stages have an annular configuration disposed around the motor. The vacuum pumping stages may be located between the rotor and the housing, thereby achieving a compact vacuum pump structure.
Each of the vacuum pumping stages may comprise a stationary member secured to the housing and a rotating member secured to the rotor of the motor. In a first embodiment, one or more of the vacuum pumping stages comprises an axial turbomolecular pumping stage, each including a stationary member having inclined blades and a rotating member having inclined blades. In a second embodiment, one or more of the vacuum pumping stages comprises a molecular drag stage, each including a stationary member having a tangential flow channel and a rotating member in the form of a disk. In a third embodiment, one or more of the vacuum pumping stages comprises a rotating member and a stationary member disposed in close proximity, one of the members having a molecular drag groove for pumping gas when the rotating member rotates relative to the stationary member.
In another embodiment, the vacuum pumping stages comprise at least one outer stage located between the rotor and the housing, and at least one inner stage located between the rotor and the stator, wherein the outer stage and the inner stage are connected in series.
The stator of the motor may comprise a central post having motor windings disposed thereon. The rotor may comprise a cylindrical element disposed around the stator. The cylindrical element has magnetic material located in alignment with the motor windings.
According to another aspect of the invention, a vacuum pump comprises a housing having an inlet port and an exhaust port, a motor disposed in the housing and a vacuum pumping stage. The motor comprises a stator and a rotor that rotates about a central axis when the motor is energized. The stator has a stator surface, and the rotor has a rotor surface that is spaced from the stator surface by a small gap. The vacuum pumping stage comprises a molecular drag groove disposed on the stator surface or the rotor surface. Gas is pumped through the molecular drag groove from the inlet port to the exhaust port when the motor is energized. The motor may have an inverted or a non-inverted configuration.
REFERENCES:
patent: 4732530 (1988-03-01), Ueda et al.
patent: 4735550 (1988-04-01), Okawada et al.
patent: 5020969 (1991-06-01), Mase et al.
patent: 5052887 (1991-10-01), Noviko et al.
patent: 5238362 (1993-08-01), Casaro et al.
patent: 5324177 (1994-06-01), Golding et al.
patent: 5370509 (1994-12-01), Golding et al.
patent: 5611660 (1997-03-01), Wong et al.
patent: 3919529 (1990-01-01), None
U.S. application No. 09/310,498, Casaro et al., filed May 12, 1999.
Fishman Bella
Van Quang
Varian Inc.
Walberg Teresa
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