Turbo-molecular pump

Details Turbo-molecular pump Turbo-molecular pump

1998-06-25

2001-12-25

Verdier, Christopher (Department: 3745)

Rotary kinetic fluid motors or pumps

Smooth runner surface for working fluid frictional contact

C415S009000

Reexamination Certificate

active

06332752

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a turbo-molecular pump for evacuating gas by using a high speed rotor.
2. Description of the Related Art
An example of a conventional turbo-molecular pump is shown in FIG.
13
. The pump is comprised of a cylindrical pump casing
14
housing a vane pumping section L
1
and a groove pumping section L
2
which are comprised of a rotor (rotation member) R and a stator (stationary member) S. The bottom portion of the pump casing
14
is covered by a base section
15
which is provided with an exhaust port
15
a.
The top portion of the pump casing
14
is provided with a flange section
14
a
for coupling the pump to an apparatus or a piping to be evacuated. The stator S comprises a stator cylinder section
16
, fixed sections of the vane pumping section L
1
and the groove pumping section L
2
.
The rotor R is comprised of a rotor cylinder section
12
attached to a main shaft
10
which is inserted into the stator cylinder section
16
. Between the main shaft
10
and the stator cylinder section
16
are constructed a drive motor
18
, an upper radial bearing
20
and a lower radial bearing
22
disposed on the upper and lower sides of the drive motor
18
respectively. Under the main shaft
10
, there is an axial bearing
24
having a target disk
24
a
at the bottom end of the main shaft
10
and upper and a lower electromagnets
24
b
on the stator side. In this; configuration, a high speed rotation of the rotor R is supported under a five coordinate active control system.
Rotor vanes
30
are provided integrally with the upper external surface of the rotor cylinder section
12
to form an impeller; and on the inside of the casing
14
, stator vanes
32
are provided in such a way to alternately interweave with the rotor vanes
30
. These vane members constitute the vane pumping section L
1
which carries out gas evacuation by cooperative action of the high speed rotor vanes
30
and the stator vanes
32
. Below the vane pumping section L
1
, the groove pumping section L
2
is
10
provided. The groove pumping section L
2
is comprised by a spiral groove section
34
having spiral grooves
34
a
on the outer surface of the bottom end of the rotor cylinder section
12
, and a spiral groove section spacer
36
surrounding the spiral groove section
34
of the stator S. The gas evacuation action of the groove pumping section L
2
is due to the dragging effect of the spiral grooves
34
a
against gases.
By providing the groove pumping section L
2
downstream of the vane pumping section L
1
, a wide-range turbo-molecular pump can be constructed so as to enable evacuation over a wide range of gas flow rates using one pumping unit. In this example, the spiral grooves of the groove pumping section L
2
are provided on the rotor side of the pump structure, but some pumps have the spiral grooves formed on the stator side of the pump structure.
Such turbo-molecular pumps are assembled as follows. Firstly, the groove pumping section spacer
36
is attached by coupling the lower surface of the step
36
a
to the protruded ring section
15
b
formed on the base section
15
. Next, the rotor R is fixed in some position, and the stator vanes
32
, which are normally split into two half sections, are clamped around to interweave between the rotor vanes
30
. This is followed by placing a stator vane spacer
38
, having steps on its top and bottom regions, on top of the clamped rotor vane
30
. This assembling step is repeated for each rotor vane
30
to complete the assembly of the stator vanes
32
around the rotor R.
Lastly, the pump casing
14
is attached by sliding it around the layered stator vane structure and fixing the flange
14
b
to the base of the stator S by fasteners such as bolts, thereby pressing the top stator vane spacer
38
firmly against the stepped surface
14
c
on the inside surface of the casing
14
and binding the entire layered assembly and the groove pumping section spacer
36
. It can be understood from this assembly structure that the peripheries of each of the stator vanes
32
are pressed together by stator vane spacers
38
located above and below, and similarly the groove pumping section spacer
36
is pressed down by the lowermost stator vane
32
, stator vane spacer
38
and the protrusion section
15
b
of the base section
15
, so that the axially applied pressing force prevents induced rotation of the stator vanes
32
and the groove pumping section spacer
36
with the rotor R in the circumferential direction.
Also, though not shown in the drawing, sometimes the groove pumping section spacer
36
is fastened to the stator cylinder section
16
of the stator S by bolts to assure the fixation.
In such turbo-molecular pumps, operational difficulties are sometimes encountered, such as abnormal rotation caused by eccentricity of rotor R, and they may be accompanied by damaging of the rotor vanes
30
. In such a case, the stator structure can also be subjected to significant circumferential or radial force by the rotor R and its debris, which may impact on not only the stator vanes
32
but the stator vane spacers
38
and the groove pumping section spacer
36
.
These abnormal operating conditions can cause not only deformation of the stator vanes
32
and spacers
36
,
38
, but can cause fracture of casing
14
and stator cylinder section
16
, or damage to their joints or severing of vacuum connections attached to the pump. Such damage and severing to any parts of the stator S cause breakage of vacuum in the whole processing system connected to and evacuated by the pump not only to damage the system facilities and in-process goods, but also to lead to accidental release of gases in the system to outside environment.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a turbo-molecular pump of high safety and reliability so that if an abnormal condition should develop on the rotor structure, it will not lead to damage to the stator or pump casing to cause loss of vacuum in a vacuum processing system.
The object has been achieved in a turbo-molecular pump comprising: a pump casing housing a stator and a rotor therein; a vane pumping section and/or a groove pumping section comprised by the stator and the rotor; and a constriction releasing structure for releasing constriction of at least a part of the stator when an abnormal torque is applied to the stator by the rotor.
Accordingly, when an abnormal torque is applied to a stator side of the pump structure due to some abnormal condition developing in the rotor structure, the constriction releasing structure acts to loosen the stator structure so that the rotation energy of the rotor is absorbed and transmission of torque to the pump casing is prevented and damage to pump casing and vacuum connection can be avoided. The constriction releasing structure is normally provided on the stator side of the pump structure, i.e., fixed vanes and structures for fixing the groove pumping section spacer to the pump casing.
The stator may be comprised of a plurality of stator elements, and the constriction releasing structure may be provided in a fixation structure for mutually fixing the stator elements.
The constriction releasing structure may be a fragile section provided on a stator side of the pump structure. Accordingly, the rotation energy of the rotor is absorbed by fracture of the fragile section, thereby reducing the effects of abnormal torque on the pump casing.
The stator element may be provided with a flange section for their fixation, and the fragile section may be formed in the flange section. Accordingly, transmission of abnormal torque to the pump casing is prevented by fracture along the fragile section in the groove pumping section in the stator which can be readily deformed outward.
In another aspect of the invention, the turbo-molecular pump comprises: a pump casing housing a stator and a rotor therein; a vane pumping section and/or a groove pumping section comprised by the stator and the rot

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