EP0829645A2

EP0829645A2 - Turbomolecular pump

Info

Publication number: EP0829645A2
Application number: EP97306652A
Authority: EP
Inventors: Yasushi Maejima
Original assignee: Seiko Seiki KK
Current assignee: Seiko Seiki KK
Priority date: 1996-09-12
Filing date: 1997-08-29
Publication date: 1998-03-18
Also published as: EP0829645A3; JPH1089284A

Abstract

In order to improve the exhaust performance of the turbomolecular pump comprising an exhaust stage, intermediate stage, and compression stage formed in sequence by rotor blades and the stator blades to effect exhaust and compression of gas, and rotor blades 141 to 144 are installed to a rotor shaft 12 supported by a bearing 20, and fixed stator blades 181 to 184 are arranged between the rotor blades, each vane of the rotor blade 144 forming the compression stage is arranged radially in a tilted manner with respect to the rotor shaft 12, and curved in the width direction so as to be convex to the rear side with respect to the vane rotation direction. Therefore, gas flows along the plate surface at the periphery of each vane 144b, so that the gas can be moved from the upper side to the lower side, thereby avoiding turbulence.

Description

The present invention relates to a turbomolecular pump used as a vacuum device such as for semiconductor manufacturing equipment and for an electron microscope.

In a turbomolecular pump rotor blades installed to a rotor shaft rotating at a high speed and stator blades fixed to a casing are arranged alternately, and a plurality of stages of pairs of rotor blade and stator blade are provided, by which an exhaust stage, intermediate stage, and compression stage are formed to effect exhaust and compression of gas in a molecular flow region.

A rotor blade 1 is, as shown in FIG. 7, made up of a ring-shaped ring portion la and a plurality of flat plate shaped vanes 1b provided radially on the outer peripheral surface of the ring portion la. As shown in FIG. 7, each of vanes 1b is tilted at a predetermined angle with respect to a rotation axis R, and the thickness thereof is substantially uniform. FIG. 8 is a partial plan view of the rotor blade 1, and FIG. 9 is a sectional view at each position in the lengthwise direction of the vane 1b.

Also, in this turbomolecular pump, although the vanes of the rotor blade differ in size and tilt angle among the exhaust, intermediate, and compression stages, the cross section thereof is in a flat plate shape as shown in FIG. 9.

With the turbomolecular pump thus configured, the rotor blade is rotated by the rotation of the rotor shaft, and the vane of the rotor blade moves gas molecules by hitting them in the rotation direction, by which exhaust is effected.

However, it is thought that the gas density on the compression stage side of turbomolecular pump is higher than the gas density on the exhaust stage side, so that the gas has the property of viscous flow; therefore, the gas is difficult to move even when an attempt is made to move the gas by "hitting" as is done on the exhaust stage side. That is to say, as shown in FIG. 10, especially the rear side (right hand side of vane in the figure) with respect to the rotation direction of vane 1b, the gas cannot move along the surface of the vane 1b, causing separation. Since this creates a stirring of the gas, an improvement in exhaust performance cannot be achieved. The load applied to a motor for rotating the rotor blades is increased by the turbulence of the gas, and therefore the motor generates a larger amount of heat than is necessary.

SUMMERY OF THE INVENTION

Accordingly, an object of the present invention is to provide a turbomolecular pump which achieves an improvement in exhaust performance and a reduction in load of the rotation generating source for rotating the rotor blades.

To achieve the above object, the present invention provides a turbomolecular pump comprising:

a rotor shaft;

a bearing for rotatably supporting said rotor shaft;

a motor for rotating said rotor shaft supported by said bearing;

a plurality of stages of rotor blades which are installed to said rotor shaft and provided with a plurality of vanes formed radially so as to tilt at a predetermined angle with respect to said rotor shaft; and

a plurality of stages of stator blades arranged between said rotor blades of plural stages;

at least one of said rotor blade stages having vanes at least some of which are formed so that each vane is curved in the width direction so as to be convex to the rear side with respect to the vane rotation direction.

Thus, in the present invention, for example, as shown in FIG. 4, each vane 144b of a rotor blade 144 is curved in the width direction so as to be convex to the rear side with respect to the rotation direction of the vane 144b.

Therefore when each vane 144b is rotated by the rotation of the rotor blade 144, gas flows along the plate surface without separation at the periphery of each vane 144b as shown in FIG. 4, so that the upper side gas can be moved to the lower side, thereby improving the exhaust performance of the turbomolecular pump as a whole.

Also, since the turbulence on the downstream side of the vane 144b is eliminated and the separation of gas is not produced, the load applied to the motor, which is a driving source for rotating the rotor blade 144, is reduced, and this reduction can prevent the heat generation of motor.

Further, in the present invention, each vane 144b of the rotor blade 144 forming the compression stage has a rounded leading edge, and the surface roughness of the surface of each vane 144b is improved, by which the above-mentioned effects are further achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a turbomolecular pump in accordance with a first embodiment of the present invention;

FIG. 2 is a partial plan view of a rotor blade at a compression stage;

FIG. 3 is a sectional view of a vane of the rotor blade;

FIG. 4 is a view for illustrating the operation of the vane;

FIG. 5 is a partial plan view of a rotor blade at a compression stage in accordance with a second embodiment of the present invention;

FIG. 6 is a sectional view of each portion of a vane of the rotor blade;

FIG. 7 is a perspective view of a rotor blade of a conventional turbomolecular pump;

FIG. 8 is a partial plan view of the rotor blade;

FIG. 9 is a sectional view of a vane of the rotor blade; and

FIG. 10 is a view for illustrating the operation of the vane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, preferred embodiments of the present invention will be described with reference to FIGS. 1 to 6.

FIG. 1 is a sectional view showing the general configuration of a turbomolecular pump in accordance with a first embodiment of the present invention. FIG. 2 is a partial plan view of a rotor blade at a compression stage of the turbomolecular pump. FIG. 3 is a sectional view of each position of a vane of the rotor blade.

As shown in FIG. 1, a turbomolecular pump 10 of this first embodiment comprises a substantially columnar rotor shaft 12, a rotor blade portion 14 installed to the rotor shaft 12, a stator blade portion 18 fixed to the inner periphery of a substantially cylindrical casing 16, a bearing 20 for supporting the rotor shaft 12 by a magnetic force, and a motor 21 for giving a torque to the rotor shaft 12.

The rotor blade portion 14 is made up of four types of

rotor blades

141, 142, 143, and 144, and the stator blade portion 18 is made up of four types of

stator blades

181, 182, 183, and 184 corresponding to the

rotor blades

141, 142, 143, and 144, respectively. The rotor blades 141 to 144 and the corresponding stator blades 181 to 184 are arranged alternately in the vertical direction with some gap lying therebetween.

By such an arrangement, for example, an exhaust stage is formed by the rotor blade 141 and the stator blade 181, an intermediate stage is formed by the

rotor blades

142 and 143 and the

stator blades

182 and 183, and a compression stage is formed by the rotor blade 144 and the stator blade 184. On the rotor blade 144 and the stator blade 184 forming the compression stage, vanes, described later, are provided more densely than the vanes of other portions to prevent the back flow of gas from an outlet port 39.

The

rotor blade

141, 142, 143 is, like the rotor blade 1 shown in FIG. 7, made up of a ring-shaped ring portion and a plurality of flat plate shaped vanes provided radially on the outer peripheral surface of the ring portion. The size and tilt angle of the vane differ among the

rotor blades

141, 142, and 143.

The

stator blade

181, 182, 183 has vanes similar to those of the

rotor blade

141, 142, 143, and the tilt direction of each vane is reverse to the tilt direction of vane of the

rotor blade

141, 142, 143.

Next, the detailed construction of the rotor blade 144 will be described with reference to FIGS. 2 to 4.

As shown in FIG. 2, the rotor blade 144 is made up of a ring-shaped ring portion 144a and a plurality of vanes 144b provided radially on the outer peripheral surface of the ring portion 144a.

As shown in FIG. 3, each vane 144b is tilted at a predetermined angle with respect to a rotation axis and curved in the width direction so as to be convex to the rear side with respect to the rotation direction of the vane 144b.

Further, as shown in FIG. 4, each vane 144b has a rounded leading edge 144b-1 and improved surface roughness of a surface 144b-2 on the rear side with respect to the vane rotation direction.

The stator blade 184 has the same construction as that of the

stator blades

181, 182, and 183. The aforesaid bearing 20 comprises

radial electromagnets

22 and 24 and an axial electromagnet 26 for producing a magnetic force in the radial direction with respect to the rotor shaft 12 and a magnetic force in the axial direction, respectively, radial sensors 30 and 32 and an axial sensor 34 for detecting the radial and axial positions of the rotor shaft 12, respectively, and a controller 36 for feedback controlling exciting current of the

radial electromagnets

22 and 24 and the axial electromagnet 26 on the basis of the detection signals of the radial sensors 30 and 32 and the axial sensor 34, respectively.

Next, the operation of the first embodiment having the above-mentioned configuration will be described with reference to the drawings.

When the turbomolecular pump 10 of this embodiment is driven, the rotor shaft 12 is kept at a predetermined floating position in a non-contact state by the bearing 20 and in this state, the rotor shaft 12 is rotated by the drive of the motor 21.

By the rotation of each rotor blade 14 between the stator blades 18, gas is sucked through an inlet port 38, compressed, and discharged through the outlet port 39 as shown in FIG. 1.

At the exhaust stage formed by the rotor blade 141 and the stator blade 181 and the intermediate stage formed by the

rotor blades

142 and 143 and the

stator blades

182 and 183, gas molecules move toward the outlet port 39 by being hit by the vanes of the

rotor blades

141, 142, and 143 because the gas flow can be handled as a molecular flow.

At the compression stage formed by the rotor blade 144 and the stator blade 184, however the gas density is high as compared with the exhaust and intermediate stages, so that the gas flow cannot be handled as a molecular flow.

In the first embodiment, each blade 144b of the rotor blade 144 forming the compression stage is curved in the width direction so as to be convex to the rear side with respect to the rotation direction of the vane 144b as shown in FIG. 3. Therefore, when each vane 144b is rotated by the rotation of the rotor blade 144, gas flows along the plate surface without separation at the periphery of each vane 144b, so that the upper side gas can be moved to the lower side, thereby improving the exhaust performance.

Also, since the turbulence on the downstream side of the vane 144b is eliminated and the separation of gas is not produced, the load applied to the motor, which is a driving source for rotating the rotor blade, is reduced, and this reduction can prevent the heat generation of motor.

Further, in this embodiment, each vane 144b has a rounded leading edge 144b-1 and improved surface roughness of the surface 144b-2, so that the exhaust performance is further improved.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 and 6.

In this second embodiment, the rotor blade 144 in accordance with the first embodiment is replaced by a rotor blade 145 as shown in FIGS. 5 and 6.

That is to say, in the second embodiment, the rotor blade 145 is made up of a ring-shaped ring portion 145a and a plurality of vanes 145b provided radially on the outer peripheral surface of the ring portion 145a as shown in FIG. 5.

As shown in FIG. 6, each vane 145b is tilted at a predetermined angle with respect to a rotation axis and curved in the width direction so as to be convex to the rear side with respect to the rotation direction of the vane 145b, and additionally each vane 145b is twisted in the lengthwise direction.

Since the construction of other portions of the second embodiment is the same as that of the first embodiment, the explanation thereof is omitted.

As described above, in the present invention, the vane of the rotor blade is curved in the width direction so as to be convex to the rear side with respect to the vane rotation direction, so that the improvement in exhaust performance and the reduction in load applied to the rotation generating source for rotor blade can be achieved.

The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims

A turbomolecular pump (10) comprising:

a rotor shaft (12);

a bearing (20) for rotatably supporting said rotor shaft;

a motor (21) for rotating said rotor shaft supported by said bearing;

a plurality of stages of rotor blades (141-144) which are installed to said rotor shaft and provided with a plurality of vanes formed radially so as to tilt at a predetermined angle with respect to said rotor shaft; and

a plurality of stages of stator blades (181-184) arranged between said rotor blades of plural stages;

at least one of said rotor blade stages having vanes (144b) at least some of which are formed so that each vane is curved in the width direction so as to be convex to the rear side with respect to the vane rotation direction.
A turbomolecular pump according to claim 1, wherein each curved vane (145b) is twisted in the lengthwise direction.
A turbomolecular pump according to claim 1 or 2, wherein each curved vane has a rounded leading edge (144b-1).
A turbomolecular pump according to claim 1, 2, or 3, wherein each curved vane has improved surface roughness of the surface on the rear side (144b-2) with respect to the vane rotation direction.
A turbomolecular pump according to any preceding claim wherein said plurality of stages of rotor blades are divided into an exhaust stage (141), an intermediate stage (142,143) and a compression stage (144), and the vanes of the compression stage are curved as aforesaid.