Pumps – Successive stages – Fluid motor for one stage supplied from another stage
Reexamination Certificate
1999-06-21
2001-04-24
Thorpe, Timothy S. (Department: 3746)
Pumps
Successive stages
Fluid motor for one stage supplied from another stage
C417S201000
Reexamination Certificate
active
06220824
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to high vacuum pumps used for evacuating an enclosed vacuum chamber and, more particularly, to compact, low cost vacuum pumps. The invention relates to improvements in prior art vacuum pumps of the type which incorporate an electric 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, 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, and strict limitations are placed on the size of the equipment. Another application requiring small size is portable instruments, such as miniature mass spectrometers. In such applications, the electric motor adds significantly to the size, weight and cost of the vacuum pump.
A prior art large capacity turbomolecular pump has been driven by a gas turbine, which in turn was driven by an air compressor. Because of the need for an air compressor, the prior art pump was expensive and required a tight rotary seal between the pump and turbine sections.
Accordingly, there is a need for vacuum pumps which are compact, which are low in cost 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 for coupling to a backing pump, one or more vacuum pumping stages disposed in the housing, each of the vacuum pumping stages comprising a stationary member and a rotating member, and a gas turbine. The gas turbine comprises a gas inlet, a gas outlet coupled to the exhaust port and a rotor coupled to the rotating members of the vacuum pumping stages. A gas flow, produced by the backing pump, through the gas turbine causes the rotor and the rotating members of the vacuum pumping stages to rotate, wherein gas is pumped by the vacuum pumping stages from the inlet port to the exhaust port.
The exhaust port of the vacuum pump may be adapted for direct coupling to a backing pump or may be adapted for coupling to a centralized vacuum system having a remotely-located backing pump.
The gas turbine may include a valve for controlling gas flow through the gas turbine. The gas turbine may include a nozzle for directing the gas flow to the rotor of the gas turbine. The nozzle inlet may operate at or below atmospheric pressure.
The gas turbine may be positioned adjacent to a last stage of the vacuum pumping stages and may be located in the same housing with the vacuum pumping stages. The rotor of the gas turbine and the rotating members of the vacuum pumping stages may be coupled to a common shaft.
In a first embodiment, at least one of the vacuum pumping stages comprises an axial turbomolecular stage wherein the rotating member and the stationary member have inclined blades. In a second embodiment, at least one of the vacuum pumping stages comprises a molecular drag stage having a stationary member that is provided with a tangential flow channel having an inlet and an outlet separated by a stationary baffle, and a rotating member comprising a disk. In a third embodiment, at least one of the vacuum pumping stages comprises a regenerative stage. In a fourth embodiment, the vacuum pumping stages comprise one or more axial turbomolecular stages and one or more molecular drag stages.
According to another aspect of the invention, a vacuum pumping system is provided. The vacuum pumping system comprises a vacuum pump including a housing having an inlet port and an exhaust port, one or more vacuum pumping stages disposed in the housing, each of the vacuum pumping stages having a stationary member and a rotating member, and a gas turbine. The gas turbine comprises a gas inlet, a gas outlet coupled to the exhaust port and a rotor coupled to the rotating members of the vacuum pumping stages. The vacuum pumping system further comprises a backing pump coupled to the exhaust port of the vacuum pump, wherein a gas flow, produced by the backing pump, through the gas turbine causes the rotor and the rotating members of the vacuum pumping stages to rotate, wherein gas is pumped by the vacuum pumping stages from the inlet port to the exhaust port
REFERENCES:
patent: Re. 33129 (1989-12-01), Mase et al.
patent: 2235763 (1941-03-01), Horton et al.
patent: 2613030 (1952-10-01), Troy
patent: 3969039 (1976-07-01), Shoulders
patent: 5074747 (1991-12-01), Ikegami et al.
patent: 5219269 (1993-06-01), Ikegami et al.
patent: 5238362 (1993-08-01), Casaro et al.
patent: 5611660 (1997-03-01), Wong et al.
patent: 5695316 (1997-12-01), Schutz et al.
patent: 3919529 (1990-01-01),
Fishman Bella
Gray Michael K.
Thorpe Timothy S.
Varian Inc.
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