Vacuum pump, cylindrical portion used in vacuum pump, and base portion

Abstract

Provided is a vacuum pump including a turbomolecular mechanism having rotor blades and stator blades alternately arranged in multiple stages in an axial direction inside a casing having an inlet port that sucks gas from an outside and an outlet port that exhausts the sucked gas to the outside, the vacuum pump including: a plurality of annular spacers that are stacked on each other and position the stator blades in the axial direction; the casing that has a cylindrical portion arranged to surround outer peripheries of the plurality of stacked spacers and a base portion attached to a lower portion of the cylindrical portion; and an upper radial positioning portion and a lower radial positioning portion provided at two vertical positions inside the cylindrical portion and coaxially hold at least a spacer of an uppermost stage and a spacer of a lowermost stage among the plurality of stacked spacers.

Claims

1. A vacuum pump including a turbomolecular mechanism having rotor blades and stator blades that are alternately arranged in multiple stages in an axial direction inside a casing having an inlet port for sucking gas from an outside and an outlet port for exhausting the sucked gas to the outside, the vacuum pump comprising: a plurality of annular spacers that are stacked on each other and position the stator blades in the axial direction; the casing that is constituted by at least two components of a cylindrical portion that is arranged to surround outer peripheries of the plurality of stacked spacers and a base portion that is attached to a lower portion of the cylindrical portion; and an upper radial positioning portion of an inner peripheral surface of the cylindrical portion and a lower radial positioning portion of the inner peripheral surface of the cylindrical portion are provided at two vertical positions inside the cylindrical portion and coaxially hold at least a spacer of an uppermost stage and a spacer of a lowermost stage among the plurality of stacked spacers and the lower radial positioning portion of the inner peripheral surface of the cylindrical portion has an inner surface in contact with an outer peripheral surface of the base portion, wherein the spacer of the uppermost stage has an inner peripheral surface facing toward an outer peripheral surface of a second-highest rotor blade of the rotor blades.

2. The vacuum pump according to claim 1, wherein the upper radial positioning portion of the inner peripheral surface of the cylindrical portion is provided corresponding to outer peripheral surfaces of the plurality of spacers, and the lower radial positioning portion of the inner peripheral surface of the cylindrical portion is provided corresponding to a lateral surface of the base portion.

3. The vacuum pump according to claim 2, wherein the upper radial positioning portion is provided corresponding to an outer peripheral surface of the spacer of the uppermost stage.

4. The vacuum pump according to claim 1, wherein each of the plurality of spacers includes a radial supporting portion that is disposed between an outer peripheral surface of each of the stator blades and an inner peripheral surface of the cylindrical portion and a spacer portion that is provided to be opposed to an outer peripheral side of each of the rotor blades and fitted and connected to an inner peripheral surface of the radial supporting portion of each of the plurality of stacked spacers adjacent to each other.

5. The vacuum pump according to claim 1, wherein the spacer of the uppermost stage includes an upper radial supporting portion that is disposed between an outer peripheral surface of a stator blade of an uppermost stage and the inner peripheral surface of the cylindrical portion, a lower radial supporting portion that is disposed between an outer peripheral surface of a stator blade that is disposed under the stator blade of the uppermost stage and the inner peripheral surface of the cylindrical portion, and a spacer portion that connects the upper radial supporting portion and the lower radial supporting portion to each other.

6. The vacuum pump according to claim 1, wherein the spacer of the uppermost stage is integrated with a stator blade of an uppermost stage.

7. The vacuum pump according to claim 2, wherein the base portion includes a cylindrical base portion that extends to an upper side in the axial direction of the casing and has the outer peripheral surface that comes into contact with the inner surface of the lower radial positioning portion and a horizontal base portion that extends in a flange shape from an outer periphery of a lower portion of the cylindrical base portion to the outside and comes into contact with a lower surface of the cylindrical portion, wherein an O-ring that seals a place between the base portion and the cylindrical portion is disposed between the horizontal base portion and the lower surface of the cylindrical portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a vertical cross-sectional view of a vacuum pump shown as an embodiment of the present invention;

(2) FIGS. 2A and 2B are enlarged views of FIG. 1, FIG. 2A being an enlarged view of a D-portion shown in FIG. 1, FIG. 2B being an enlarged view of an E-portion shown in FIG. 1;

(3) FIG. 3 is a cross-sectional view of a spacer in the vacuum pump shown in FIG. 1;

(4) FIG. 4 is a vertical cross-sectional view of a vacuum pump shown as a first modified example of the present invention;

(5) FIG. 5 is an enlarged view of an F-portion shown in FIG. 4;

(6) FIG. 6 is a vertical cross-sectional view of a vacuum pump shown as a second modified example of the present invention;

(7) FIG. 7 is a vertical cross-sectional view showing a conventional vacuum pump;

(8) FIG. 8 is an enlarged view of an H-portion shown in FIG. 7; and

(9) FIG. 9 is an enlarged cross-sectional view of a spacer in the conventional vacuum pump shown in FIG. 7.

DETAILED DESCRIPTION

(10) In order to achieve the object of providing a vacuum pump having a structure that allows the securement of the certain positioning accuracy of spacers and a reduction in a manufacturing cost for a vacuum pump even if a dimensional tolerance in manufacturing is slightly loosened, a cylindrical portion used in the vacuum pump, and a base portion, the present invention realizes a vacuum pump including a turbomolecular mechanism having rotor blades and stator blades that are alternately arranged in multiple stages in an axial direction inside a casing having an inlet port for sucking gas from an outside and an outlet port for exhausting the sucked gas to the outside, the vacuum pump including: a plurality of annular spacers that are stacked on each other and position the stator blades in the axial direction; the casing that is constituted by at least two components of a cylindrical portion that is arranged to surround outer peripheries of the plurality of stacked spacers and a base portion that is attached to a lower portion of the cylindrical portion; and radial positioning portions that are provided at two vertical positions inside the cylindrical portion and coaxially hold at least a spacer of an uppermost stage and a spacer of a lowermost stage among the plurality of stacked spacers.

(11) Hereinafter, embodiments for carrying out the present invention will be described in detail on the basis of the accompanying drawings. Note that the same elements will be denoted by the same symbols throughout the entire description of the embodiments. Further, expressions showing directions such as a top-bottom direction and a left-right direction are not absolute but are appropriate when the respective portions of a vacuum pump according to the present invention take postures drawn in the figures. However, the expressions should be interpreted in different ways according to the changes of the postures when the postures are changed.

EMBODIMENTS

(12) FIG. 1 is a vertical cross-sectional view of a vacuum pump 10 shown as an embodiment of the present invention. FIGS. 2A and 2B are partially-enlarged views of FIG. 1. FIG. 2A is an enlarged view of a D-portion shown in FIG. 1. FIG. 2B is an enlarged view of an E-portion shown in FIG. 1.

(13) In FIG. 1, the vacuum pump 10 includes a casing 11 that forms the housing of the vacuum pump 10, a rotor 13 that has a rotor shaft 12 rotatably supported inside the casing 11, a driving motor 14 that rotates the rotor shaft 12, and a stator column 15 that accommodates a portion of the rotor shaft 12 and the driving motor 14.

(14) The casing 11 has a cylindrical portion 11A and a base 11B provided beneath the cylindrical portion 11A and forms the enclosure of the vacuum pump 10.

(15) The cylindrical portion 11A of the casing 11 is formed as a cylindrical body having openings on its upper and lower sides and uses its upper opening as a gas inlet port 16. Further, an upper flange portion 17 is integrally formed on the outer periphery of the upper opening, and a lower flange portion 18 is integrally formed on the outer periphery of the lower opening. Further, an annular recessed portion 18a for an O-ring that positions and arranges an O-ring 19 for sealing is formed on the lower surface of the lower flange portion 18. On the other hand, an upper radial positioning portion (also called an “upper positioning portion”) 20 is provided at the upper portion of the cylindrical portion 11A, and a lower radial positioning portion (also called a “lower positioning portion”) 21 is provided at the lower portion of the cylindrical portion 11A on the inner peripheral surface side of the cylindrical portion 11A.

(16) The upper radial positioning portion 20 includes a first annular wall portion 20a that horizontally protrudes to an inner side from an inner peripheral surface 11AC of the cylindrical portion 11A and a second annular wall portion 20b that is perpendicularly recessed toward an upper side from the inner surface of the first annular wall portion 20a and horizontally protrudes to the inner side from its recessed position.

(17) The lower radial positioning portion 21 uses a portion of the inner peripheral surface 11AC, that is, a lower inner peripheral surface in the cylindrical portion 11A.

(18) The base 11B of the casing 11 integrally has a cylindrical base portion 22 that extends to an upper side in the axial direction of the casing 11 and has an outer peripheral surface 22a fitted and connected to the inner surface (inner peripheral surface 11AC) of the lower radial positioning portion 21 of the cylindrical portion 11A and a horizontal base portion 23 that horizontally extends in a flange shape toward an outer side from the lower periphery of the cylindrical base portion 22 and has an annular shape to come into contact with the lower surface of the lower flange portion 18 in the cylindrical portion 11A. Note that a small-diameter portion 22b to which the lower portion of a first radial supporting portion 39a of an annular spacer 39 that will be described later is attached is provided at the upper portion of the cylindrical base portion 22.

(19) Then, when the cylindrical base portion 22 and the cylindrical portion 11A are fitted to each other from the lower end of the cylindrical portion 11A, the casing 11 is connected to the base 11B with the cylindrical portion 11A placed on the base 11B as shown in FIG. 1. Further, in this connection, an O-ring 19 for sealing is interposed between the lower flange portion 18 and the horizontal base portion 23, and the lower flange portion 18 and the horizontal base portion 23 are fixed to each other by bolts 25. Thus, the cylindrical portion 11A and the base 11B are integrated with each other.

(20) The rotor 13 includes a rotor shaft 12 and rotor blades 26 that are fixed to the upper portion of the rotor shaft 12 and concentrically arranged in parallel with respect to an axial line O1 of the rotor shaft 12. In the present embodiment, the rotor blades 26 of ten stages are provided.

(21) The rotor blades 26 include blades inclined at a prescribed angle and are integrated with the upper outer peripheral surface of the rotor 13. Further, the rotor blades 26 are radially provided at a plurality places about the axial line O1 of the rotor 13.

(22) The rotor shaft 12 is supported by magnetic bearings 27 in a non-contact manner. The magnetic bearings 27 include radial electromagnets 28 and axial electromagnets 29. The radial electromagnets 28 and the axial electromagnets 29 are connected to a controlling unit not shown.

(23) The controlling unit controls exciting currents for the radial electromagnets 28 and the axial electromagnets 29 on the basis of values detected by the radial displacement sensors 28a and an axial displacement sensor 29a. Thus, the rotor shaft 12 is supported in a floating state at a prescribed position.

(24) The upper and lower portions of the rotor shaft 12 are inserted into touchdown bearings 30. When the rotor shaft 12 becomes uncontrollable, the rotor shaft 12 that rotates at a high speed comes into contact with the touchdown bearings 30 to prevent excessive damage inside the vacuum pump 10.

(25) The rotor 13 is integrally attached to the rotor shaft 12 in such a manner that bolts 32 are inserted into a rotor flange 33 and screwed into a shaft flange 34 with the upper portion of the rotor shaft 12 inserted into a boss hole 31. Hereinafter, the axial direction of the rotor shaft 12 will be called an “axial direction M,” and the radial direction thereof will be called a “radial direction R.”

(26) The driving motor 14 includes a rotor 35 that is attached to the outer periphery of the rotor shaft 12 and a stator 36 that is arranged to surround the rotor 35. The stator 36 is connected to the above controlling unit not shown, and the rotation of the rotor 13 is controlled by the controlling unit.

(27) The stator column 15 is fixed to the base 11B via bolts 37 in a state of being placed on the base 11B.

(28) Stator blades 38 are provided near the rotor blades 26 in the axial direction. That is, the rotor blades 26 and the stator blades 38 are arranged alternately and in multiple stages along the axial direction M. In the present embodiment, the stator blades 38 of ten stages are provided.

(29) The stator blades 38 are formed into an annular shape and include blades that are inclined in a direction opposite to the direction of the rotor blades 26 and rings that are connected to both ends of the blades. The stator blades 38 are held by spacers 39 stacked on each other on the inner peripheral surface of the cylindrical portion 11A of the casing 11 and positioned in the axial direction M and the radial direction R. Further, the blades of the stator blades 38 are radially provided at a plurality of places about the axial line O1 of the rotor 13.

(30) Further, a gas outlet port 24 that is in communication with the outside is provided on the outer peripheral surface of the cylindrical base portion 22 of the base 11B. The gas outlet port 24 is connected so as to communicate with an auxiliary pump not shown. On the basis of the mutual action between the rotor blades 26 and the stator blades 38, the vacuum pump 10 transfers gas (air) G sucked in from the gas inlet port 16 from an upper side to a lower side in the axial direction M and exhausts the same to the outside from the gas outlet port 24.

(31) The stator blade 38 of the lowermost stage is placed on the small-diameter portion 22b of the cylindrical base portion 22 in the base 11B. Specifically, the base end of the stator blade 38 is held by the cylindrical base portion 22, the upper surface of the small-diameter portion 22b, and the spacer 39 to be supported in the axial direction M and the radial direction R.

(32) The spacers 39 are stator members having a substantially cylindrical shape and extend along the axial direction of the casing 11. The spacers 39 include first radial supporting portions 39a that orbit and oppose the outer peripheral surfaces of the stator blades 38 and oppose the inner peripheral surface 11AC of the cylindrical portion 11A with a slight gap placed therebetween and second radial supporting portions 39b that orbit and oppose the outer peripheral surfaces of the rotor blades 26 and come into contact with the inner peripheral surfaces of the first radial supporting portions 39a. Further, small-diameter portions (step portions) 39c to which the lower portions of the first radial supporting portions 39a of the spacers 39 that are sequentially stacked on an upper side are attached are formed on the outer peripheries of the second radial supporting portions 39b.

(33) Note that a recessed amount in the radial direction of the small-diameter portions 39c in the spacers 39 is substantially equal to a thickness in the radial direction of the first radial supporting portions 39a and set so that the outer peripheral surfaces of the spacers 39 stacked on an upper side and the outer peripheral surfaces of the spacers 39 on a lower side are flush with each other when the lower portions of the first radial supporting portions 39a of the spacers 39 stacked on the upper side are attached to the small-diameter portions 39c. On the other hand, a recessed amount in the radial direction on the inner peripheral surface side of the first radial supporting portions 39a in the spacers 39 is substantially equal to a thickness in the radial direction of the second radial supporting portions 39b and set so that the inner peripheral surfaces of the spacers 39 stacked on an upper side and the inner peripheral surfaces of the spacers 39 on a lower side are substantially flush with each other when the upper portions of the second radial supporting portions 39b stacked on the lower side spacer 39 are attached to the first radial supporting portions 39a. Further, a height in the axial direction of the respective spacers 39 is arbitrarily set in proportion to the heights (thicknesses) of the blades of the rotor blades 26 and the stator blades 38.

(34) Then, in the assembling of the stator blades 38 and the spacers 39 of the vacuum pump 10, the stator blade 38 of the lowermost stage is first placed on the small-diameter portion 22b of the cylindrical base portion 22 in the base 11B after the rotor 13 that serves as a rotating portion is installed on the base 11B, and the spacer 39 of the lowermost stage is next stacked on the stator blade 38 of the lowermost stage. At this time, the spacer 39 of the lowermost stage is attached in a state of enclosing the stator blade 38 of the lowermost stage and the small-diameter portion 22b inside the first radial supporting portion 39a. Thus, the small-diameter portion 22b and the first radial supporting portion 39a are fitted and connected to each other to position the spacer 39 of the lowermost stage with respect to the base 11B. Further, when the spacer 39 of the lowermost stage is arranged, the rotor blade 26 of the lowermost stage is enclosed by this spacer 39 in a non-contact state.

(35) Next, the stator blade 38 of the second stage is placed on the second radial supporting portion 39b of the spacer 39 of the last stage, and then the spacer 39 of the second stage is stacked on the stator blade 38 of the second stage. At this time, the spacer 39 of the second stage is attached in a state of enclosing the stator blade 38 of the second stage and the second radial supporting portion 39b of the spacer 39 of the lowermost stage inside the first radial supporting portion 39a. The second radial supporting portion 39b of the spacer 39 of the lowermost stage and the first radial supporting portion 39a of the spacer 39 of the second stage are fitted and connected to each other to position the spacer 39 of the second stage with respect to the spacer 39 of the lowermost stage. Further, when the spacer 39 of the second stage is arranged, the rotor blade 26 of the last stage is enclosed by the spacer 39 in a non-contact state. When the above operation is repeatedly performed, a gas transfer mechanism 40 having the cylindrical stator portion and the rotor portion in which the rotor blades 26 and the stator blades 38 are alternately arranged in multiple stages in the axial direction is assembled and formed.

(36) After the assembling of the stator blades 38 and the spacers 39, the casing 11 is put from above the side of the spacer 39 of the uppermost stage. Thus, the gas transfer mechanism 40 is accommodated in the casing 11. Note that in the operation of accommodating the gas transfer mechanism 40 in the casing 11, the casing 11 is dropped using the gas transfer mechanism 40 as a guide in a state in which the spacer 39 of the uppermost stage is inserted from the lower opening of the cylindrical portion 11A. At this time, the casing 11 is dropped with the inner peripheral surface 11AC of the cylindrical portion 11A sliding against the outer peripheral surfaces of the spacers 39. Then, when the casing 11 is dropped into a position right before its final position, the lower radial positioning portion 21 that is provided on the inner peripheral surface 11AC of the cylindrical portion 11A comes into contact with the outer peripheral surface 22a of the cylindrical base portion 22 and the lower side of the gas transfer mechanism 40 is positioned with respect to the base 11B. Further, when the casing 11 is dropped into its substantially final position, the upper radial positioning portion 20 provided on the inner peripheral surface 11AC of the cylindrical portion 11A corresponds to the spacer 39 of the uppermost stage. Thus, the upper portion of the spacer 39 of the uppermost stage is fitted and connected to the first annular wall portion 20a and the second annular wall portion 20b, and the upper side of the gas transfer mechanism 40 is positioned with respect to the casing 11. That is, the two vertical positions of the gas transfer mechanism 40 are positioned by the upper radial positioning portion 20 and the lower radial positioning portion 21, and the movement or inclination in the radial direction R of the whole of the spacers 39 arranged in multiple stages is prevented (reduced).

(37) In the vacuum pump 10 thus configured, the upper flange portion 17 of the casing 11 that has the gas inlet port 16 as described above is attached to a vacuum container such as a chamber not shown, and the auxiliary pump not shown is attached to the gas outlet port 24 that is provided on the base 11B. When the driving motor 14 of the vacuum pump 10 is driven in this state, the rotor blades 26 rotate at a high speed together with the rotor 13. Thus, gas G from the gas inlet port 16 is flowed into the vacuum pump 10, sequentially transferred inside the gas transfer mechanism 40, and exhausted from the gas outlet port 24 of the base 11B. That is, the inside of the vacuum container is evacuated.

(38) Accordingly, the vacuum pump 10 of this embodiment is so structured that the two vertical positions of the gas transfer mechanism 40 are positioned by the upper radial positioning portion 20 and the lower radial positioning portion 21 and the movement or inclination in the radial direction of the whole of the spacers 39 arranged in multiple stages is prevented. Therefore, the movement or inclination in the radial direction R of the whole of the spacers 39 arranged in multiple stages is prevented (reduced). Thus, even if processing accuracy (tolerance) in the manufacturing of the casing 11 and the spacers 39 is slightly loosened, certain positioning accuracy is securable. Therefore, the manufacturing or the like of the casing 11 and the spacers 39 is facilitated. As a result, a reduction in a manufacturing cost is allowed. Note that in conventional structures in which only the upper position of a gas transfer mechanism is positioned, the respective tolerances of a dimension A of the inner peripheries of first radial supporting portions, a dimension B of the outer peripheries of spacers, and a dimension C of the outer peripheries of small-diameter portions (step portions) are requested to be small and tightened. Compared with the conventional structures, the present invention makes it possible to loosen the tolerances by about 30%. Therefore, processing is simplified, and a reduction in a manufacturing cost is allowed.

(39) FIG. 4 is a vertical cross-sectional view of a vacuum pump 10 shown as a first modified example of the vacuum pump shown in FIG. 1. In the first modified example shown in FIG. 4, a spacer 139 of the uppermost stage is deformed, and the other configurations are the same as those of the vacuum pump 10 shown in FIG. 1 and FIGS. 2A and 2B. Therefore, the same constituting portions will be denoted by the same symbols, and their duplicated descriptions will be omitted.

(40) The annular spacer 139 of the uppermost stage shown in FIG. 4 is arranged on the outer peripheral surface of a stator blade 38(38a) of the uppermost stage, the outer peripheral surface of a stator blade right under the stator blade 38a of the uppermost stage, that is, a stator blade 38(38b) of the second-highest stage, and the outer peripheral surface of a rotor blade 26a of the second-highest stage. The spacer 139 of the uppermost stage includes a spacer portion 139d that holds an interval in an axial direction between the stator blade 38(38a) of the uppermost stage and the stator blade 38(38b) of the second-highest stage, a first radial supporting portion 139a that vertically extends from the outer peripheral edge of the lower surface of the spacer portion 139d to a lower side in the axial direction and serves as a lower radial supporting portion, and a second radial supporting portion 139b that vertically extends from the outer peripheral edge of the upper surface of the spacer portion 139d to an upper side in the axial direction and serves as an upper radial supporting portion.

(41) Then, in a state of enclosing the stator blade 38b of the second-highest stage with the first radial supporting portion 139a and enclosing the rotor blade 26 of the second-highest stage with the spacer portion 139d, the spacer 139 of the uppermost stage is fitted and connected to a small-diameter portion (step portion) 139c of a spacer 39 of the second-highest stage. Thus, the spacer 139 of the uppermost stage is stacked on the spacer 39 of the second-highest stage to be positioned. After that, a stator blade 38a of the uppermost stage is placed on the upper surface of the spacer portion 139d of the spacer 139 of the uppermost stage, and then a cylindrical portion 11A of a casing 11 is put on the spacers 139.

(42) Further, in a state in which the cylindrical portion 11A is put on the spacers 139, an upper radial positioning portion 20 provided on the inner peripheral surface 11AC of the cylindrical portion 11A corresponds to the spacer 139 of the uppermost stage, the upper portion of the spacer 139 of the uppermost stage comes into contact with and fits into a first annular wall portion 20a, and the upper surface of the spacer 139 of the uppermost stage comes into contact with a second annular wall portion 20b. Thus, the upper side of a gas transfer mechanism 40 is positioned with respect to the casing 11. On the other hand, a lower radial positioning portion 21 of the casing 11 comes into contact with an outer peripheral surface 22a of the cylindrical base portion 22 and positions the lower side of the gas transfer mechanism 40 with respect to the base 11B.

(43) Accordingly, also in the vacuum pump 10 shown as the first modified example, the two vertical positions of the gas transfer mechanism 40 are positioned by the upper radial positioning portion 20 and the lower radial positioning portion 21, and the movement or inclination in a radial direction of the whole of the spacers 39 arranged in multiple stages is prevented. Thus, the structure of this modified example makes it possible to save space to orbit and oppose the rotor blade 26 of the uppermost stage and reduce a manufacturing cost since the number of components of the vacuum pump 10 of this modified example is smaller than that of the vacuum pump 10 shown in FIG. 1.

(44) FIG. 6 is a vertical cross-sectional view of a vacuum pump 10 shown as a second modified example of the vacuum pump shown in FIGS. 1, 2A and 2B. In the second modified example shown in FIG. 6, a spacer 239 of the uppermost stage is integrated with a stator blade 238 of the uppermost stage, and the other configurations are the same as those of the vacuum pump 10 shown in FIG. 1 and FIGS. 2A and 2B. Therefore, the same constituting portions will be denoted by the same symbols, and their duplicated descriptions will be omitted.

(45) The annular spacer 239 of the uppermost stage shown in FIG. 6 is an annular member and integrated with the stator blade 238 of the uppermost stage that extends substantially horizontally from the inner peripheral surface of the spacer 239 of the uppermost stage to an axial line O1. Further, a first radial supporting portion 239a that is fitted and connected to a second radial supporting portion 39b of a spacer 39 of the second-highest stage is provided at the lower portion of the spacer 239, and a second radial supporting portion 239b that comes into contact a first annular wall portion 20a and a second annular wall portion 20b of an upper radial positioning portion 20 to be positioned and engaged and serves as a radial positioning portion is provided at the upper portion of the spacer 239.

(46) Further, in a state of enclosing a rotor blade 26 of the uppermost stage with the second radial supporting portion 239b, the spacer 239 of the uppermost stage makes the first radial supporting portion 239a fitted and connected to a small-diameter portion (step portion) 39c of the spacer 39 of the second-highest stage. Thus, the spacer 239 of the uppermost stage is stacked on the spacer 39 of the second-highest stage to be positioned. After that, a cylindrical portion 11A of a casing 11 is put on the spacers.

(47) Further, in a state in which the cylindrical portion 11A of the casing 11 is put on the spacers, the upper radial positioning portion 20 provided on an inner peripheral surface 11AC of the cylindrical portion 11A corresponds to the spacer 239 of the uppermost stage. The upper portion of the spacer 239 of the uppermost stage is fitted and connected to the first annular wall portion 20a, and the upper surface of the second radial supporting portion 239b comes into contact with the second annular wall portion 20b. Thus, the upper side of a gas transfer mechanism 40 is positioned with respect to the casing 11. On the other hand, a lower radial positioning portion 21 of the casing 11 comes into contact with an outer peripheral surface 22a of a cylindrical base portion 22 and positions the lower side of the gas transfer mechanism 40 with respect to a base 11B.

(48) Accordingly, also in the vacuum pump 10 shown as the second modified example, the two vertical positions of the gas transfer mechanism 40 are positioned by the upper radial positioning portion 20 and the lower radial positioning portion 21, and the movement or inclination in a radial direction of the whole of the spacers 39 arranged in multiple stages is prevented. Further, the structure of this second modified example makes it possible to reduce a manufacturing cost since the spacer 239 of the uppermost stage is integrated with the stator blade 238 of the uppermost stage and thus the number of components of the vacuum pump 10 of this second modified example is smaller than that of the vacuum pump 10 shown in FIG. 1.

(49) Note that the present invention may be modified in various ways without departing from its spirit and applied to the modifications as a matter of course.

(50) Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

(51) Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.