Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Reexamination Certificate
2002-10-22
2004-12-21
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
C415S173100, C415S129000
Reexamination Certificate
active
06832888
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a molecular pump and, more specifically, to a molecular pump for exhausting or evacuating a chamber or container by the use of a thread groove pump stage.
2. Description of the Related Art
There is a growing need for a pump having a high exhaust capability and being able to achieve a high degree of vacuum with recent accelerated advance in scientific technology.
A molecular pump is widely used in the academic field or in the industrial field as a pump meeting such requirements of the users.
The molecular pump includes a thread groove pump, a turbo molecular pump, or the combination thereof.
FIG. 11
is an illustration of a structure of a molecular pump in the related art, constructed of a turbo molecular pump on the inlet port side and a thread groove pump on the exhaust port side.
A molecular pump
101
includes a turbo molecular pumping stage
102
and a thread groove pumping stage
103
. Gas sucked through an inlet port
104
is compressed in the turbo molecular pumping stage
102
, and then further compressed in the thread groove pumping stage
103
, and finally discharged from an exhaust port
105
.
The molecular pump
101
includes a rotor shaft
106
, and the rotor shaft
106
is rotatably supported by magnetic bearings
107
,
108
,
109
about the axis. The magnetic bearings
107
,
108
allow magnetic levitation of the rotor shaft
106
in the radial direction and a magnetic bearing
109
allows magnetic levitation of the rotor shaft
106
in the thrust direction.
The rotor shaft
106
includes a motor unit
110
substantially on the axial midsection thereof, and torque generated by the motor unit
110
allows fast axial rotation thereof.
A rotor
111
is secured on the rotor shaft
106
on the side of the inlet port
104
by means of a bolt. The rotor
111
includes a turbine section constituting a body of revolution of the turbo molecular pumping stage
102
and a cylindrical section
122
constituting a body of revolution of the thread groove pumping stage
103
.
The turbine section is formed with a number of rotor vanes
112
of multiple stages in the radial direction. A casing
114
is formed with stator vanes
113
of multiple stages on the inner peripheral surface thereof so as to be directed toward the rotor shaft
106
and arranged alternately between the rotor vanes
112
.
A thread groove spacer
116
is disposed around the outer peripheral surface of a cylindrical section
122
having a cylindrical outer peripheral surface with a predetermined clearance therefrom. The thread spacer
116
has a cylindrical inner peripheral surface, on which a thread groove
120
is formed in a helical manner.
The molecular pump
101
constructed as described above operates as follows.
After magnetic levitation of the rotor shaft
106
is effected by the magnetic bearings
107
,
108
,
109
, the motor unit
110
is driven to rotate the rotor
111
and gas is sucked through the inlet port
104
. Sucked gas is compressed in the turbo molecular pumping stage
102
and fed to the thread groove pumping stage
113
by the action of the rotor vanes
112
and the stator vanes
113
. In the thread groove pumping stage
103
, gas is guided through the thread groove
120
as a flow path along the cylindrical section
122
rotating at high-velocity, and is further compressed while being carried downwardly. In this manner, gas sucked through the inlet port
104
is compressed in the turbo molecular pumping stage
102
, and then further compressed in the thread groove pumping stage
103
, and finally discharged from the exhaust port
105
.
In this manner, the reason why two types of molecular pump are combined is that the optimal pump differs depending on the pressure range. Accordingly, a molecular pump having a high compression ratio may be realized by constructing the front stage of gas compression of the turbo molecular pumping stage
102
and the rear stage of the thread groove pumping stage
103
.
FIG. 12
shows a connecting state between the molecular pump
101
and a chamber
126
in the related art.
When the turbo molecular pump
101
is connected to the chamber
126
to which gas is discharged, the turbo molecular pump
101
may be connected via a gate valve
125
. The gate valve
125
is disposed for adjusting the pressure in the chamber
126
, and is capable of adjusting the pressure in the chamber
126
by adjusting the opening of the gate valve
125
while operating the turbo molecular pump
101
.
However, in the thread groove pumping stage
103
in the related art, a clearance
121
between the rotor
122
and the surface opposed thereto is set to a certain value (for example, 1 mm) or more for ensuring safety and hence preventing the thread groove pumping stage
103
and the rotor
122
from coming into contact. As a result when the gas pressure discharged by the pump is increased, a backflow of gas may characteristically occur through the clearance
121
between the rotor
122
and the surface opposing thereto, which results in lowering of performance.
On the other hand, though there were market requirements to control the pressure by controlling exhaust capability of the pump, the only way was to change the revolution of the rotor
111
in the related art. However, changing the revolution of the rotor is time consuming and, as a result, the pressure of the chamber
126
is controlled by means of the expensive gate valve
125
, which results in increase in costs.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a molecular pump having a minimum clearance
12
, having high gas compressibility, and being capable of controlling gas compressibility.
According to the invention, gas compressibility may be increased, and gas compressibility may be controlled in a molecular pump.
According to the invention, in order to achieve the object described above, there is provided a molecular pump including a stator, a rotor having an opposing surface that faces toward a predetermined surface of the stator and being rotatably supported with the opposing surface faced toward the surface, a motor for driving and rotating the rotor with respect to the stator, a thread groove formed on at least one of the surfaces of the stator and the rotor that face toward each other, a transport device for transporting gas through the thread groove by rotating the rotor by the motor, and a clearance varying device for varying the magnitude of the clearance between the opposing surfaces of the stator and the rotor (first structure).
The first structure may be achieved by providing a device that is capable of varying the magnitude of the clearance between the rotor and the surface opposed thereto as desired at the thread groove section of the thread groove pump or the turbo molecular pump. The clearance varying device allows setting of the magnitude of the clearance by means of a mechanism that moves the rotor or the surface opposing thereto in the axial direction by varying the floating position of the magnetic bearing. A thread groove is formed on at least one of the opposing surfaces of the rotor and the stator, so that gas is transported through the thread groove while being compressed with the rotation of the rotor.
The first structure may be such that the bus line of the surface of the rotor that faces toward the stator forms a predetermined angle, which is larger than zero degree at the smallest, with respect to the axis of the rotor, and the clearance varying device varies the magnitude of the clearance by moving at least one of the rotor and the stator in the direction of the axis of the rotor (second structure).
If the angle formed between the bus line and the axis is zero degree, the opposing surfaces of the rotor and the stator become cylindrical and if it is 90, the opposing surfaces of the rotor and the stator become disk shape. When it is a predetermined angle but not zero degree, the opposing surfaces becomes substantially cylindrical such as the outer peripheral surface o
Kabasawa Takashi
Miwata Tooru
Nonaka Manabu
Adams & Wilks
BOC Edwards Technologies Limited
Kershteyn Igor
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