VACUUM PUMP, AND ROTOR AND ROTOR BLADE FOR USE IN VACUUM PUMP

Abstract

A vacuum pump includes: a casing formed with an inlet port or outlet port; a stator disposed inside the casing; and a rotor enclosed in the casing and including a shaft rotatably supported on the stator, and a rotor blade formed in a cylindrical shape with a plurality of blades arranged in multiple stages on an outer circumferential portion thereof, and secured to the shaft such as to be integrally rotatable therewith. The rotor blade is provided with a rupture location control groove as a rupture location control means that locally reduces rigidity of the rotor blade to control a location where the rotor blade ruptures.

Claims

1. A vacuum pump comprising: a casing formed with an inlet port or an outlet port; a stator portion disposed inside the casing; and a rotor enclosed in the casing and including a shaft rotatably supported on the stator portion, and a rotor blade formed in a cylindrical shape with a plurality of blades arranged in multiple stages on an outer circumferential portion thereof, and secured to the shaft such as to be integrally rotatable therewith, the rotor blade being provided with a rupture location control means that locally reduces rigidity of the rotor blade to control location where the rotor blade ruptures.

2. The vacuum pump according to claim 1, wherein the rupture location control means is a groove provided on an outer circumferential surface of the rotor blade along an axial direction of the rotor blade between the blades adjoining each other in the axial direction.

3. The vacuum pump according to claim 1, wherein the rupture location control means is a groove provided on an inner circumferential surface of the rotor blade along an axial direction of the rotor blade.

4. The vacuum pump according to claim 1, wherein the rupture location control means is a groove provided on at least one of an outer circumferential surface or an inner circumferential surface of the rotor blade along a circumferential direction of the rotor blade.

5. The vacuum pump according to claim 2, wherein the groove is provided to each correspond to each of a plurality of bolt holes provided to the rotor blade for attaching the rotor blade to the shaft.

6. A rotor rotatably attached to a stator portion that is disposed inside a casing, which is formed with an inlet port or an outlet port, of a vacuum pump, the rotor comprising: a shaft rotatably supported on the stator portion; a rotor blade formed in a cylindrical shape, with a plurality of blades arranged in multiple stages on an outer circumferential portion thereof, and secured to the shaft such as to be integrally rotatable therewith; and a rupture location control means that is provided to the rotor blade and locally reduces rigidity of the rotor blade to control location where the rotor blade ruptures.

7. A rotor blade rotatably attached, via a shaft, to a stator portion that is disposed inside a casing, which is formed with an inlet port or an outlet port, of a vacuum pump, the rotor blade comprising: a cylindrical member formed in a cylindrical shape, with a plurality of blades arranged in multiple stages on an outer circumferential portion thereof; and a rupture location control means that is provided to the cylindrical member and locally reduces rigidity of the cylindrical member to control location where the cylindrical member ruptures.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a plan view of a vacuum pump illustrated as one embodiment of the present invention;

[0033] FIG. 2 is a longitudinal cross-sectional side view along line A-A of FIG. 1;

[0034] FIG. 3 is a plan view of a rotor blade used in the vacuum pump illustrated in FIG. 1 and FIG. 2;

[0035] FIG. 4 is a longitudinal cross-sectional side view along line B-B of FIG. 3;

[0036] FIG. 5 is a cross-sectional view explaining one example of a groove as a rupture location control means in the vacuum pump;

[0037] FIG. 6 is a cross-sectional view explaining a variation example of the groove as a rupture location control means in the vacuum pump;

[0038] FIG. 7 is a cross-sectional view explaining another variation example of the groove as a rupture location control means in the vacuum pump;

[0039] FIG. 8 is a plan view of a vacuum pump illustrated as another embodiment of the present invention;

[0040] FIG. 9 is a longitudinal cross-sectional side view along line C-C of FIG. 8;

[0041] FIG. 10 is a plan view of a rotor blade used in the vacuum pump illustrated in FIG. 8 and FIG. 9; and

[0042] FIG. 11 is a longitudinal cross-sectional side view along line D-D of FIG. 10.

DETAILED DESCRIPTION

[0043] The present invention was made to achieve an object of providing a vacuum pump with an inexpensive structure that exhibits consistent shock absorption performance wherein rupture occurs at a planned location in a planned manner in the event of a higher instantaneous torque than expected that rotates a rotor in its rotating direction being generated; as well as a rotor and a rotor blade for use in the vacuum pump. The invention achieved the object by providing a vacuum pump including: a casing formed with an inlet port or an outlet port; a stator portion disposed inside the casing; and a rotor enclosed in the casing and including a shaft rotatably supported by the stator portion, and a rotor blade formed in a cylindrical shape with a plurality of blades arranged in multiple stages on an outer circumferential portion thereof, and secured to the shaft such as to be integrally rotatable therewith, the rotor blade being provided with a rupture location control means that locally reduces rigidity of the rotor blade to control location where the rotor blade ruptures.

Embodiments

[0044] Hereinafter, an example of embodiment of the present invention will be described in detail with reference to the accompanying drawings. Where a number of constituent elements, value, quantity, or range is mentioned in the following embodiment, it is not intended to limit it to a specific value, unless otherwise explicitly indicated and unless it is clearly limited to the specific value in principle, and the number, value, quantity, or range may be more than or less than the specific value.

[0045] Where a shape of a constituent element or a positional relationship between elements is mentioned, it should be understood to include substantially approximate or similar shapes and the like, unless otherwise explicitly indicated and unless other options are clearly excluded in principle.

[0046] The drawings may exaggerate a characteristic feature by enlargement or otherwise for easier understanding of the feature, and may not necessarily illustrate the constituent elements in the same size and proportion as actual elements. In some cross-sectional views, hatching for some constituent elements may be omitted for easier understanding of a cross-sectional structure of a constituent element.

[0047] Expressions indicative of directions such as up and down or left and right in the following description should not be taken as absolutes. The expressions may be suitable for a vacuum pump of the present invention when various components are in their illustrated postures, but when their postures change, the expressions should be interpreted differently in accordance with the change in posture. Throughout the description of embodiment, same elements are given the same reference numerals.

[0048] FIG. 1 and FIG. 2 illustrate one embodiment of a vacuum pump 10 according to the present invention. FIG. 1 is a plan view and FIG. 2 is a longitudinal cross-sectional side view along line A-A of FIG. 1.

[0049] The vacuum pump 10 illustrated in FIG. 1 and FIG. 2 is a composite pump equipped with a molecular pump system 10A as a gas exhaust system, and a screw thread pump system 10B. The vacuum pump 10 is used as a gas exhaust means of a process chamber in, for example, a semiconductor manufacturing apparatus, flat panel display manufacturing apparatus, or solar panel manufacturing apparatus, or other sealed chambers.

[0050] As illustrated in FIG. 1, the vacuum pump 10 includes a casing 11. As illustrated in FIG. 2, the casing 11 is made up of a tubular pump case 11A integrated with a pump base 11B in a direction of its tube axis by fastening members 12, and has a substantially cylindrical shape with a bottom.

[0051] An upper end side (upper side in the paper plane of FIG. 2) of the pump case 11A is open as an inlet port 13, and as illustrated in FIG. 2, the pump base 11B is provided with an outlet port 14. A flange 15 is formed to the inlet port 13, and a flange 16 is formed to the outlet port 14. A sealed chamber (not shown) with a high degree of vacuum such as a process chamber or the like of a semiconductor manufacturing apparatus, for example, is connected to the flange 15 of the inlet port 13, while an auxiliary pump or the like (not shown) is connected to the flange 16 of the outlet port 14 for fluid communication.

[0052] A structure that exhibits an exhaust function is accommodated inside the casing 11 so that a gas inside the sealed chamber is sucked into the inlet port 13 and expelled from the outlet port 14. This way, the sealed chamber can be exhausted of a reaction gas for the manufacture of semiconductors, for example, or other gases. While FIG. 1 and FIG. 2 show a structure in which the vacuum pump 10 is arranged vertically, the vacuum pump 10 may be oriented horizontally and attached to a side of a sealed chamber, or the inlet port 13 may be oriented downward and attached to an upper portion of a sealed chamber.

[0053] More particularly, the structure that exhibits the exhaust function is roughly composed of a rotatably supported rotor 17 and a stator 18 fixed to the casing 11.

[0054] The rotor 17 is made up of a rotor blade 19, a shaft 20, and others.

[0055] The rotor blade 19 has a cylindrical member 21, which integrally forms a first cylindrical portion 21a disposed on the side where there is the inlet port 13 (molecular pump system 10A) and a second cylindrical portion 21b disposed on the side where there is the outlet port 14 (thread screw pump system 10B) as illustrated not only in FIG. 1 and FIG. 2 but also in FIG. 3 and FIG. 4.

[0056] The first cylindrical portion 21a is a substantially cylindrical member and forms a rotor portion 17a of the molecular pump system 10A. As illustrated in FIG. 1, FIG. 3, and FIG. 4, a plurality of blades 22 extend radially from an outer circumferential surface of the first cylindrical portion 21a outward in a plane perpendicular to an axis of the rotor blade 19 and shaft 20 and are substantially equally spaced apart in a rotating direction. Each blade 22 is inclined in the same direction at a predetermined angle relative to the horizontal direction. The first cylindrical portion 21a is formed with a plurality of stages of these radially extending sets of blades 22 at an predetermined interval along the axial direction.

[0057] As illustrated in FIG. 2 and FIG. 4, a partition wall 23 is formed in a midway point along the axial direction of the first cylindrical portion 21a for connection with the shaft 20. The partition wall 23 is formed with a shaft hole 23a for an upper end side of the shaft 20 to be inserted and attached, and bolt holes 23b for mounting bolts 24 to be attached to secure the shaft 20. Eight bolt holes 23b are circumferentially equally spaced on a concentric circle drawn around the shaft hole 23a. The number of the bolt holes 23b is not limited to this.

[0058] The second cylindrical portion 21b is a member having a cylindrical outer circumferential surface and forms a rotor portion 17b of the screw thread pump system 10B.

[0059] The shaft 20 is a columnar member that forms a shaft of the rotor 17, formed integrally with a flange portion 20a in an upper end portion thereof as illustrated in FIG. 2, which is screwed to the partition wall 23 of the first cylindrical portion 21a by the mounting bolts 24. Accordingly, the flange portion 20a is provided with eight mounting holes (not shown) corresponding to the bolt holes 23b in the partition wall 23. The shaft 20 is secured and integrated with the cylindrical member 21 by inserting the upper end portion into the shaft hole 23a from inside of the first cylindrical portion 21a (from below) until the flange portion 20a integral with the shaft 20 contacts a lower surface of the partition wall 23, after which the mounting bolts 24 are screwed into the mounting holes of the flange portion 20a through the bolt holes 23b from an upper side of the partition wall 23.

[0060] A permanent magnet is fixedly attached to an outer circumferential surface in a midway point along the axial direction of the shaft 20 and forms a portion on the rotor 17 side of a motor portion 25. This permanent magnet forms magnetic poles around the circumference of the shaft 20, the N pole extending over half the circumference of the outer circumferential surface and the S pole extending over the remaining half of the circumference.

[0061] Moreover, at the upper end side (inlet port 13 side) of the shaft 20 is formed a rotor 17 side part of a magnetic bearing portion 26 for supporting the shaft 20 in a radial direction relative to the motor portion 25, while at the lower end side (outlet port 14 side) is formed, similarly, a rotor 17 side part of a magnetic bearing portion 27 for supporting the shaft 20 in the radial direction relative to the motor portion 25. Further, a rotor 17 side part of a magnetic bearing portion 28 is formed at the lower end of the shaft 20 for supporting the shaft 20 in the axial direction (thrust direction).

[0062] Near the magnetic bearing portions 26 and 27 are provided rotor 17 side portions of displacement sensors 29 and 30, respectively, so that a displacement in the radial direction of the shaft 20 can be detected.

[0063] Further, a rotor 17 side portion of a displacement sensor 31 is provided at the lower end of the shaft 20 so that a displacement in the axial direction of the shaft 20 can be detected.

[0064] These rotor 17 side parts of the magnetic bearing portions 26 and 27 and the displacement sensors 29 and 30 are formed by laminated steel plates in which steel plates are stacked in the shaft direction of the rotor 17. This is for preventing an eddy current from being generated in the shaft 20 by magnetic fields created by coils that form stator 18 side parts of the magnetic bearing portions 26 and 27 and the displacement sensors 29 and 30.

[0065] The rotor 17 described above is composed using metal such as stainless steel and aluminum alloy.

[0066] The first cylindrical portion 21a of the rotor blade 19 in the rotor 17 is provided with rupture location control grooves 32 as rupture location control means.

[0067] The rupture location control grooves 32 include, as illustrated in FIG. 1 to FIG. 4, first rupture location control grooves 32a formed on an outer circumferential surface along the axial direction of the first cylindrical portion 21a, and a second rupture location control groove 32b formed along an outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b as illustrated in FIG. 2 and FIG. 4.

[0068] The first rupture location control grooves 32a are substantially equally spaced apart in the circumferential direction between blades 22 adjoining each other in the axial direction, as well as along the axial direction of the rotor blade 19, on the outer circumferential surface of the first cylindrical portion 21a. The first rupture location control grooves 32a are 5.8 mm in width and 8 to 15 mm in depth, for example, which may vary depending on the material and thickness of the cylindrical member 21, and have a semicircular concave curved cross-sectional shape as illustrated in FIG. 5. The rotor blade 19 is reduced in thickness and lowered in mechanical strength in locations where the first rupture location control grooves 32a of the first cylindrical portion 21a are provided compared to other parts of the first cylindrical portion 21a where the first rupture location control grooves 32a are not provided. Accordingly, in the event of a higher torque than expected being generated and applied on the rotor 17, the rotor blade 19 ruptures in locations where the first rupture location control grooves 32a are provided along the axial direction on the outer circumferential surface of the first cylindrical portion 21a in a planned manner along the axial direction, and this rupture can absorb the shock of torque on the entire vacuum pump 10.

[0069] The second rupture location control groove 32b is formed horizontally substantially all around the outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b. Similarly to the first rupture location control grooves 32a, the second rupture location control groove 32b is 5.8 mm in width and 8 to 15 mm in depth, for example, which may vary depending on the material and thickness of the cylindrical member 21, and has a semicircular concave curved cross-sectional shape similarly to the first rupture location control grooves 32a. With the second rupture location control groove 32b around the outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b, the rotor blade 19 is reduced in thickness and lowered in mechanical strength in the location where the second rupture location control groove 32b is provided to the cylindrical member 21 compared to other parts where the groove is not provided, similarly to the case with the first rupture location control grooves 32a. Accordingly, in the event that a higher torque than expected is generated and this torque is applied on the rotor 17, the cylindrical member 21 ruptures in a planned location that is substantially along a boundary between the first cylindrical portion 21a and the second cylindrical portion 21b (portion indicated by a one-dot chain line and denoted at 33 in FIG. 4, hereinafter referred to as “boundary 33”) where the second rupture location control groove 32b is provided around the outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b. The cylindrical member 21 then splits into the first cylindrical portion 21a and second cylindrical portion 21b, and this rupture can absorb the shock of torque.

[0070] The stator 18 is formed on the inner circumference of the casing 11. The stator 18 is made up of a stator blade 34 provided on the side where there is the inlet port 13 (molecular pump system 10A), and a screw thread spacer 35 provided on the side where there is the outlet port 14 (screw thread pump system 10B).

[0071] The stator blade 34 is made up of blades inclined at a predetermined angle from a plane perpendicular to the axis of the shaft 20 and extending from an inner circumferential surface of the casing 11 toward the shaft 20. A plurality of stages of the stator blades 34 are formed along the axial direction in the molecular pump system 10A such as to alternate with the blades 22 of the rotor blade 19. The stages of the stator blades 34 are spaced apart from each other by cylindrical spacers 36.

[0072] The screw thread spacer 35 is a columnar member formed with a spiral groove 35a on an inner circumferential surface thereof. The inner circumferential surface of the screw thread spacer 35 opposes the outer circumferential surface of the second cylindrical portion 21b of the cylindrical member 21 with a predetermined clearance (gap) therebetween. The spiral groove 35a formed on the screw thread spacer 35 is oriented in such a direction that when a gas is transported in the spiral groove 35a in the rotating direction of the rotor 17, the gas will travel toward the outlet port 14. The spiral groove 35a has a depth that reduces toward the outlet port 14 so that the gas transported in the spiral groove 35a is compressed as it approaches the outlet port 14.

[0073] The stator 18 is composed using metal such as stainless steel and aluminum alloy.

[0074] The pump base 11B is a disc-shaped member, with a cylindrical stator column 37 oriented toward the inlet port 13 and attached in the center of the radial direction concentrically with the rotating axis of the rotor 17. The stator column 37 supports the stator side parts of the motor portion 25, magnetic bearing portions 26 and 27, and displacement sensors 29 and 30.

[0075] In the motor portion 25, a predetermined number of poles are arranged on the inner circumference of the stator coil at equal distance so that a rotating magnetic field can be generated around the magnetic poles formed on the shaft 20. On the outer circumference of the stator coil is arranged a collar 38, which is a cylindrical member made of metal such as stainless steel, to protect the motor portion 25.

[0076] The magnetic bearing portions 26 and 27 are formed by coils arranged at every 90 degrees around the rotating axis. These coils of the magnetic bearing portions 26 and 27 generate magnetic fields that attract the shaft 20, so that the shaft 20 is magnetically levitated in the radial direction.

[0077] The magnetic bearing portion 28 is formed at the bottom of the stator column 37. The magnetic bearing portion 28 is formed by a disc extending out from the shaft 20 and coils arranged on and under this disc. These coils generate magnetic fields that attract this disc, so that the shaft 20 is magnetically levitated in the axial direction.

[0078] The inlet port 13 of the casing 11 is formed with a flange 15 extending out radially beyond the pump case 11A. The flange 15 is formed with bolt holes 39 for bolts (not shown) to pass through, and a groove 40 for mounting an O-ring to keep a seal between itself and a flange on the vacuum container side (not shown).

[0079] The vacuum pump 10 configured as described above operates as follows to exhaust a vacuum container of a gas.

[0080] First, the magnetic bearing portions 26, 27, and 28 magnetically levitate the shaft 20 to support the rotor 17 in space in a non-contact manner.

[0081] Next, the motor portion 25 is activated to rotate the rotor 17 in a predetermined direction. The rotation speed is about 30,000 rotations per minute, for example. In this embodiment, the rotating direction of the rotor 17 is the clockwise direction indicated by the arrow line R in FIG. 1 when viewed from the direction of the arrow line E in FIG. 2. The vacuum pump 10 can also be designed to rotate in the counterclockwise direction.

[0082] When the rotor 17 rotates, the gas is sucked into the inlet port 13 by the action of the blades 22 of the rotor blade 19 and the stator blades 34 of the stator 18, and is compressed as it travels down to the lower stages. After compressed in the molecular pump system 10A, the gas is further compressed in the screw thread pump system 10B, and expelled from the outlet port 14.

[0083] Next, a process when a higher torque than expected is generated in the rotor 17 of the vacuum pump 10 configured as described above, and when this torque is applied on the rotor 17, will be described.

[0084] In the vacuum pump 10 of this embodiment, a plurality of first rupture location control grooves 32a and a second rupture location control groove 32b are provided on the outer circumferential surface of the first cylindrical portion 21a. The rotor blade 19 is reduced in thickness and lowered in mechanical strength in the locations where these first rupture location control grooves 32a and second rupture location control groove 32b are provided compared to other parts where the first rupture location control grooves 32a and second rupture location control groove 32b are not provided. Accordingly, in the event of a higher torque than expected being generated and applied on the rotor 17, rupture occurs at the locations of the first rupture location control grooves 32a and/or second rupture location control groove 32b in a planned manner along these grooves, whereby the first cylindrical portion 21a and second cylindrical portion 21b are separated into several pieces, and this separation absorbs the shock of torque. Here, for example, the first cylindrical portion 21a cracks along each of the plurality of first rupture location control grooves 32a, ruptures along the axial direction, and breaks apart into several pieces, and/or, the first cylindrical portion 21a and second cylindrical portion 21b rupture in the circumferential direction along the boundary 33 shown in FIG. 4 therebetween and break apart into several pieces. Namely, rupture occurs in a planned manner in planned locations which are the first rupture location control grooves 32a and/or second rupture location control groove 32b, so that a process after the rupture can be readily carried out in a preset procedure. This allows for consistent maintenance work and inexpensive processing.

[0085] The first rupture location control grooves 32a as rupture location control means are provided such as to each correspond to each of the plurality of bolt holes 23b that are provided for secure attachment of the shaft 20 via bolts. The portions where the first rupture location control grooves 32a are provided and the portions where the bolt holes 23b are provided are weaker and lower in mechanical strength than other parts. Therefore, when a higher torque than expected is generated and applied on the rotor 17, rupture easily occurs in a planned manner not only at the first rupture location control grooves 32a but also at a location where a first rupture location control groove 32a is aligned with a bolt hole 23b, so that rupture that occurs at this location also absorbs the shock of torque. Thus the process after the rupture can be readily carried out in a preset procedure.

[0086] While the embodiment described above has shown a structure in which the first rupture location control groove 32a and second rupture location control groove 32b have a semicircular concave curved cross-sectional shape as illustrated in FIG. 5, the shape is not limited to such a semicircular concave curve. For example, the grooves may have a square recessed shape as illustrated in FIG. 6, or a V-shaped recessed shape as illustrated in FIG. 7.

[0087] FIG. 8 to FIG. 11 illustrate a variation example of the vacuum pump 10 according to the present invention. FIG. 8 is a plan view, FIG. 9 is a longitudinal cross-sectional side view along line C-C of FIG. 8, FIG. 10 is a plan view of a rotor blade 19 used in the vacuum pump illustrated in FIG. 8 and FIG. 9, and FIG. 11 is a longitudinal cross-sectional side view along line D-D of FIG. 10. Compared to the first rupture location control grooves 32a in the vacuum pump 10 of the embodiment illustrated in FIG. 1 to FIG. 7, which are substantially equally spaced apart circumferentially on the outer circumferential surface of the first cylindrical portion 21a and extend along the axial direction of the rotor blade 19, the first rupture location control grooves in the variation example illustrated in FIG. 8 to FIG. 11 are substantially equally spaced apart circumferentially on an inner circumferential surface of the first cylindrical portion 21a, and extend along the axial direction of the rotor blade 19. Other configurations are the same as those shown in FIG. 1 to FIG. 4, and same structural elements are given the same reference numerals to avoid repetitive description.

[0088] The part having a different structure from that of the embodiment illustrated in FIG. 1 to FIG. 4 is that, first rupture location control grooves 132a of the rupture location control grooves 32 are formed on the inner circumferential surface along the axial direction of the first cylindrical portion 21a, and a second rupture location control groove 32b of the rupture location control groove 32 is formed along an outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b similarly to the embodiment illustrated in FIG. 1 to FIG. 4.

[0089] The first rupture location control grooves 132a are substantially equally spaced apart circumferentially on the inner circumferential surface of the first cylindrical portion 21a, and extend along the axial direction of the rotor blade 19 as illustrated in FIG. 8 to FIG. 11. The first rupture location control grooves 132a here are 5.8 mm in width and 8 to 15 mm in depth, for example, which may vary depending on the material and thickness of the cylindrical member 21. By providing the first rupture location control grooves 132a, the rotor blade 19 is reduced in thickness and lowered in mechanical strength in locations where the first rupture location control grooves 132a are provided compared to other parts where the grooves are not provided. Moreover, the first rupture location control grooves 132a are provided such as to each correspond to each of the plurality of bolt holes 23b that are provided for secure attachment of the shaft 20 via bolts. Therefore, the portions where the first rupture location control grooves 132a are provided and the portions where the bolt holes 23b are provided are designed to be weaker and lower in mechanical strength than other parts. Accordingly, in the event of a higher torque than expected being generated in the rotor 17 and applied on the rotor 17, the rotor blade 19 ruptures in a planned manner along the axial direction at locations where the first rupture location control grooves 132a are provided along the axial direction on the inner circumferential surface of the first cylindrical portion 21a, and this rupture can absorb the shock of torque.

[0090] In the variation example illustrated in FIG. 8 to FIG. 11, too, a plurality of first rupture location control grooves 132a are provided on the inner circumferential surface of the first cylindrical portion 21a, substantially equally spaced apart circumferentially and along the axial direction of the rotor blade 19, as well as a second rupture location control groove 32b is provided along the outer circumference at the lower end of the first cylindrical portion 21a adjacent the second cylindrical portion 21b such as to horizontally surround the outer circumference of the first cylindrical portion 21a substantially all around. The rotor blade 19 is reduced in thickness and lowered in mechanical strength in the locations where these first rupture location control grooves 132a and second rupture location control groove 32b are provided compared to other parts where the first rupture location control grooves 132a and second rupture location control groove 32b are not provided. Accordingly, in the event of a higher torque than expected being generated and applied on the rotor 17, rupture occurs at the locations of the first rupture location control grooves 132a and/or second rupture location control groove 32b in a planned manner along these grooves, whereby the first cylindrical portion 21a and second cylindrical portion 21b are separated into several pieces, and this separation absorbs the shock of torque. Here, for example, the first cylindrical portion 21a cracks along each of the plurality of first rupture location control grooves 132a, ruptures along the axial direction, and breaks apart into several pieces, and/or, the first cylindrical portion 21a and second cylindrical portion 21b rupture in the circumferential direction along the boundary 33 shown in FIG. 4 therebetween and break apart into several pieces. Namely, rupture occurs in a planned manner in planned locations which are the first rupture location control grooves 132a and/or second rupture location control groove 32b, so that the process after the rupture can be readily carried out in a preset procedure. This allows for consistent maintenance work and inexpensive processing.

[0091] While this variation example shows a structure for the vacuum pump 10 in which the second rupture location control groove 32b is formed horizontally substantially all around the outer circumference of the first cylindrical portion 21a, an alternative structure is also possible wherein the groove extends horizontally on the inner circumference of the first cylindrical portion 21a substantially all around.

[0092] The first rupture location control grooves 132a as rupture location control means are provided such as to each correspond to each of the plurality of bolt holes 23b that are provided for secure attachment of the shaft 20 via bolts. Therefore, the portions where the first rupture location control grooves 132a are provided and the portions where the bolt holes 23b are provided are weaker and lower in mechanical strength than other parts. Accordingly, in the event of a higher torque than expected being generated in the rotor 17 and applied on the rotor 17, rupture occurs in a planned manner at the first rupture location control grooves 132a and at a location where a first rupture location control groove 132a is aligned with a bolt hole 23b, and absorbs the shock of torque. Thus the process after the rupture can be readily carried out in a preset procedure.

[0093] While this variation example has also shown a structure in which the first rupture location control groove 132a and second rupture location control groove 32b have a semicircular-curved cross-sectional shape, the shape is not limited to such a semicircular-curved section. For example, the grooves may have a square-shaped section, or a V-shaped section.

[0094] Further, it goes without saying that various modifications can be made to the present invention without departing from the spirit of the present invention, and that the present invention covers such modifications.

[0095] 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.

[0096] 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.