US20130129482A1

US20130129482A1 - Vacuum pump

Info

Publication number: US20130129482A1
Application number: US13/813,345
Authority: US
Inventors: Shingo TSUTSUI
Original assignee: Shimadzu Corp
Current assignee: Shimadzu Corp
Priority date: 2010-08-06
Filing date: 2011-08-05
Publication date: 2013-05-23
Also published as: WO2012018111A1; JPWO2012018111A1; JP5494807B2; CN103069173A; CN103069173B

Abstract

A vacuum pump (1) includes: a rotor (30) provided with a rotor-side discharge function unit (32); a motor (36) that drives the rotor (30) to rotate with respect to a stator-side discharge function unit (22); and a cylindrical pump casing (2) made of a magnetic material, in which the rotor (30) and the stator-side discharge function unit (22) are disposed.

Description

TECHNICAL FIELD

The present invention relates to a vacuum pump including a rotor that rotates at a high speed and being suitable for use in a magnetic field.

BACKGROUND ART

A turbomolecular pump discharges gas by rotating a rotor provided with turbine blades with respect to stator turbine blades at high speeds. The stator turbine blades and the rotor are disposed in a pump casing provided with an inlet flange (refer to, for example, Patent Literature 1).

CITATION LIST

Patent Literature

PATENT LITERATURE 1: Japanese Laid-open Patent Publication No. 2008-038844.

SUMMARY OF INVENTION

Technical Problem

The turbomolecular pump includes a pump casing that generally comprises austenite stainless steel (for example, SUS304), which is excellent in corrosion resistance and tensile strength in view of corrosion resistance in case a corrosive gas is discharged and of safety upon breakage of the rotor and so on. However, if the turbomolecular pump is used in magnetic fields, the pump casing is pervious to lines of magnetic force since the austenite stainless steel is a non-magnetic material, so that eddy current is generated in the rotor that rotates at high speeds. As a result, the rotor is overheated due to Joule heat and there is the possibility that the creep rupture of the rotor, which is made of an aluminum alloy, will result.

Solution to Problem

According to the 1st aspect of the present invention, a vacuum pump comprises: a rotor provided with a rotor-side discharge function unit; a motor that drives the rotor to rotate with respect to a stator-side discharge function unit; and a cylindrical pump casing made of a magnetic material, in which the rotor and the stator-side discharge function unit are disposed.
According to the 2nd aspect of the present invention, in the vacuum pump according to the 1st aspect, it is preferred that the rotor-side discharge function unit includes a plurality of stages consisting of rotor turbine blades disposed in an inner space of the pump casing, and a cylindrical drag pump rotating portion provided at a downstream side of the stages consisting of rotor turbine blades outside the inner space of the pumping casing, and the stator-side discharge function unit includes a plurality of stages consisting of stator turbine blades, and a cylindrical drag pump fixing portion which is disposed so as to surround an outer circumferential surface of the drag pump rotating portion at a gap therefrom and which is made of a magnetic material.
According to the 3rd aspect of the present invention, in the vacuum pump according to the 1st or the 2nd aspect, it is preferred that the vacuum pump further comprises: a magnetic bearing unit that includes a thrust magnetic bearing that supports the rotor in an axial direction and a radial bearing that supports the rotor in a radial direction, a pump base portion that is provided with the magnetic bearing unit and that is made of a non-magnetic material, an axial sensor that detects a position in the axial direction of the rotor, a radial sensor that detects a position in the radial direction of the rotor, a first magnetic shield member that is made of a magnetic material and that is provided at an inlet of the pump casing to reduce entrance of external magnetic field into the pump via the inlet, and a second magnetic shield member that is made of a magnetic material and that is provided at the pump base portion to reduce influence of external magnetic field on the magnetic bearing unit.
According to the 4th aspect of the present invention, in the vacuum pump according to the 3rd aspect, it is preferred that the second magnetic shield member constitutes a vacuum container in which at least the axial sensor is housed.
According to the 5th aspect of the present invention, in the vacuum pump according to the 4th aspect, it is preferred that the vacuum pump further comprises: a third magnetic shield member made of a magnetic material that extends in the direction of from the second magnetic shield member to the pump casing so as to cover an outer circumferential surface of the pump base portion that is made of the non-magnetic material.
According to the 6th aspect of the present invention, in the vacuum pump according to the 5th aspect, it is preferred that the second magnetic shield member and the third magnetic shield member are formed into a one body
According to the 7th aspect of the present invention, in the vacuum pump according to any one of the 3rd to 6th aspects, it is preferred that the magnetic shield member includes a disc portion and a supporting beam that supports the disc portion at a center of the inlet.
According to the 8th aspect of the present invention, in the vacuum pump according to the 7th aspect, it is preferred that the rotor includes a plurality of stages consisting of turbine blades as the rotor-side discharge function unit, the disc portion has an outer diameter D, which is not smaller than an outer diameter Ds of the radial sensor and not larger than a diameter Dri of a circle that passes a joint of each of the turbine blades in a circumferential direction of the rotor.
According to the 9th aspect of the present invention, in the vacuum pump according to any one of the 1st to 8th aspects, it is preferred that the vacuum pump further comprises: a protective net that is fastened to the inlet of the pump casing with bolts to prevent foreign matter from entering the pump, the pump casing being formed of threaded through-holes for fastening with bolts.
According to the 10th aspect of the present invention, in the vacuum pump according to any one of the 3rd to 6th aspects, it is preferred that the first magnetic shield member serves as the protective net that is provided at the inlet of the pump casing and prevents foreign matter from entering the pump.
According to the 11th aspect of the present invention, in the vacuum pump according to any one of the 1st to 10th aspect, it is preferred that the magnetic material includes a carbon steel or an alloy steel.
According to the 12th aspect of the present invention, in the vacuum pump according to the 11th aspect, it is preferred that the pump casing is made of S45C as the carbon steel.
According to the 13th aspect of the present invention, in the vacuum pump according to the 11th or 12th aspect, it is preferred that a surface of the magnetic material is subjected to anticorrosion treatment including N—P plating treatment.

Advantageous Effect of Invention

According to the present invention, the stability of the vacuum pump with respect to external magnetic fields, such as prevention of overheating of the rotor due to eddy current and so on can be increased.

BRIEF DESCRIPTION OF DRAWINGS

(FIG. 1) A cross-sectional view of a pump body 1 that constitutes a turbomolecular pump;

(FIG. 2) A schematic diagram that illustrates the state of lines of magnetic force when the pump body 1 is disposed in an external magnetic field;

(FIG. 3) A diagram showing the tensile strength of a representative magnetic material;

(FIG. 4) A diagram showing the tensile strength of alloy steel for a machine structure;

(FIG. 5) A diagram showing the tensile strength of carbon steel for a machine structure;

(FIG. 6) A diagram showing a thread hole 200 for fixing a protective net;

(FIG. 7) A diagram showing a pump casing 2 surrounding both a turbomolecular pump unit and a drag pump unit;

(FIG. 8) A diagram illustrating a second embodiment;

(FIG. 9) A fragmentary view taken in the direction of arrow A in FIG. 8;

(FIG. 10) A diagram illustrating actions of thrust covers 40 and 41 and a magnetic shield member 42;

(FIG. 11) A diagram showing a variation example of the second embodiment; and

(FIG. 12) A diagram showing a variation example of the magnetic shield member 42.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the embodiments of the present invention are explained with reference to the attached drawings.

First Embodiment

FIG. 1 is a diagram showing a first embodiment of a vacuum pump according to the present invention, showing a cross-sectional view of a pump body 1 that constitutes a turbomolecular pump. The turbomolecular pump includes the pump body 1 shown in FIG. 1 and a control unit (not shown).
The turbomolecular pump shown in FIG. 1 is a magnetically suspended turbomolecular pump, in which a rotor 30 is contactlessly supported by magnetic bearings 37 in the radial direction and magnetic bearings 38 in the thrust direction. A suspended position of the rotor 30 at which it is suspended is detected by a radial displacement sensor 27 and axial displacement sensor 28. The rotor 30, which is magnetically suspended rotatably by the magnetic bearings, is driven by a motor 36 to rotate at high speeds. Reference numerals 26, 29 denote mechanical bearings. When the magnetic bearings are not operating, the mechanical bearings 26, 29 support the rotor 30.
The turbomolecular pump according to the present embodiment includes a turbo pump unit and a drag pump unit as discharge function units. The turbo pump unit is constituted by a plurality of stages consisting of rotor blades 32 provided in the rotor 30 and a plurality of stages consisting of stator blades 22 alternately disposed with respect to the rotor blades in the axial direction. The drag pump unit is constituted by a cylindrical portion 31 provided in the rotor 30 and a thread stator 24 disposed so as to surround the cylindrical portion 31 at a predetermined gap therefrom. It should be noted that the rotor blades 32 and the cylindrical portion 31 constitute a discharge function unit on the rotor-side and the stator blades 22 and the thread stator 24 constitute a discharge function unit on the stator-side.
The rotor 30 and the stator blades 22 are disposed in the inside of the cylindrical pump casing 2 made of a magnetic material. Each of the stator blades 22 is mounted on a base 20 via a spacer ring 23. When a fixed flange 21 c of the pump casing 2 is fastened to the base 20 with a bolt, a stacked spacer ring 23 is sandwiched between the base 20 and the pump casing 2 to position the stator blade 22. The base 20 is provided with a discharge port 25, to which is connected a back pump. By driving the rotor 30 to rotate at high speeds by a motor 36 while the rotor 30 is being magnetically suspended, gas molecules on the side of the inlet 21 a are discharged to the side of the discharge port 25.
On the side of the inlet of the pump casing 2, an inlet flange 21 b is provided. The inlet flange 21 b is formed of inlets 21 a, through which gas molecules flow into the pump. When the pump body 1 is attached to a vacuum apparatus, generally, the inlet flange 21 b is fastened to a flange on the side of the apparatus with bolts. The inlet flange 21 b is formed of a plurality of bolt holes for fitting bolts therein. The number of bolt holes and diameter of bolt holes are set according to standards of the flange. Also, to the inlet flange 21 b is fastened a protective net 8 for preventing foreign matter from coming into the pump.
The rotor of a turbomolecular pump generally includes an aluminum alloy and in case the turbomolecular pump is used in a magnetic field, a problem arises that eddy current is generated therein under influence of the magnetic field. FIG. 2 is a diagram schematically showing the state of lines of magnetic force when the pump body 1 is disposed in an external magnetic field, showing B-B cross-section in FIG. 1. In FIG. 2, (a) shows a conventional turbomolecular pump and (b) shows a turbomolecular pump according to the present embodiment. A solid line denoted by reference numeral 100 shows lines of magnetic force due to the external magnetic field. On the other hand, a symbol R indicates the rotation direction of the rotor 30.
Semiconductor manufacturing apparatus and liquid crystal panel manufacturing apparatus in which turbomolecular pumps are used are frequently operated for discharging corrosive gases. To provide against possible breakage of the rotor 30 that rotates at high speeds, the pump casing 2 needs to be made of a material that has excellent tensile strength. For this purpose, the conventional turbomolecular pumps use austenite stainless steel, for example SUS304 and so on as a material that is excellent in corrosion resistance and has high tensile strength. However, since the austenite stainless steel is a non-magnetic material, if the turbomolecular pump is used in a magnetic field, a magnetic field should be inevitably formed in a space in the pump casing 2 in which the rotor 30 is disposed. As a result, when the rotor 30 is rotated at high speeds in the magnetic field, eddy current is generated, so that there arises the problem that the temperature of the rotor 30 is increased due to Joule heat caused by the eddy current.
On the other hand, in the case of the turbomolecular pump according to the present embodiment, the pump casing 2 is formed with a magnetic material having high permeability, so that the lines of magnetic force concentrate on the pump casing 2 and the space in the pump casing is magnetically shielded by the pump casing 2. As a result, the rotor 30 is scarcely influenced by the external magnetic field, and the generation of eddy current is prevented.
As mentioned above, it is necessary that the pump casing 2 is made of a material having high tensile strength. As an index to be used here, the tensile strength (about 520 MPa) of the conventionally used austenite stainless steel (SUS304) is referred to. FIG. 3 shows the tensile strength of representative magnetic materials. Among them, Permalloy and steels for mechanical structures have tensile strength equivalent to or higher than 520 MPa of SUS304.
FIG. 4 shows the tensile strength of alloy steels for mechanical structures (JIS G 4053) and FIG. 5 shows the tensile strength of carbon steels for mechanical structures (JIS G 4051). In the case of the alloy steels for mechanical structures shown in FIG. 4, each of them has a tensile strength not lower than 700 MPa, which is above the tensile strength (520 MPa) of SUS304. That is, the alloy steels for mechanical structures can be used in place of SUS304. Among the carbon steels for mechanical structures shown in FIG. 5, S45C and S55C with high carbon contents have tensile strength higher than that of SUS304. If a material that has tensile strength comparable to SUS304 is to be selected, S45C shown in FIG. 5 is appropriate.
Since it is required that the pump casing 2 has corrosion resistance, it is necessary to form a corrosion resistant protective film on the surface of the pump casing if the materials shown in FIGS. 4 and 5 are used. Examples of the corrosion resistant protective film include films formed by plating such as nickel plating or electrodeposition coating. From the point of corrosion resistance, nickel plating is preferred.
In the case of turbomolecular pumps, it is generally adopted to attach a protective net 8 as shown in FIG. 1 to the inlet in order to prevent foreign matter from coming into the pump. FIG. 6 is a diagram shown thread holes 200 for fixing the protective net that is formed in the inlet flange portion of the pump casing 2. As shown in FIG. 1, the protective net 8 that prevents intake of the foreign matter is arranged at the inlet 21 a of the pump casing 2. The protective net 8 is fastened to the inlet flange 21 b with bolts. The inlet flange 21 b is formed of the thread holes 200 with which bolts 201 are threadably mounted. According to the present embodiment, in order to increase the throwing power of plating to the thread holes 200, the thread holes 200 are threaded through-holes.
For the bolts 201 for fastening the protective net, bolts as small as possible, for example bolts of M3 or so are used in order to increase the opening area of the inlet 21 a. For this reason, in case the thread holes 200 are not through-holes, the thickness of the plating becomes thinner toward the back of the holes and there is the possibility that no plating is applied to the bottom portion of the thread holes. In such a case, even if the bolts 201 are threadably mounted, the corrosive gas could go around the back of the thread holes 200, so that there is the possibility that the pump casing 2 will get rusted. However, the occurrence of such inconvenience can be prevented by providing through-holes as shown in FIG. 6. Also, by using carbon steels in place of conventional SUS304, the pump casing 2 can be manufactured at relatively low cost.
In the example illustrated in FIG. 1, the pump casing 2 is provided so as to surround the outer periphery of the turbo pump. However, the pump casing may be configured to surround both the turbo pump unit (22, 32) and the drag pump unit (24, 31). This can further increase the magnetic shielding effect of the pump casing 2 on the rotor 30.
It is also possible to make the pump casing 2 to have a shape similar to that shown in FIG. 1 and the thread stator 24 to be made of a magnetic material similar to that used for the pump casing 2. With this configuration, the cylindrical portion 31 of the rotor 30 is magnetically shielded by the thread stator 24. Also, in this case, the thread stator 24 is made of a magnetic material and is formed of a corrosion resistant protection film such as nickel plating.

Second Embodiment

The turbomolecular pump shown in FIG. 8 has a basic structure as a pump that is the same as the structure shown in FIG. 1, however, is different from the structure shown in FIG. 1 in that the former includes a thrust cover 40, a thrust cover 41 and a magnetic shield member 42. Although the construction of the magnetic bearings is shown in detail in FIG. 8, their structures are the same as those of the magnetic bearings in the pump shown in FIG. 1.
In the turbomolecular pump according to the first embodiment, a configuration of the pump is adopted such that, when an external magnetic field in the radial direction acts on the pump, generation of eddy current is prevented in the side circumferential portion of the rotor 30 (for example, the cylindrical portion 31). However, there is the possibility that when an external magnetic field in the axial direction acts on the pump, eddy current is generated in the rotary blades 32 of the rotor 30. Separately from heat generation due to eddy current, there arises a problem of an influence of the external magnetic field on the control of magnetic bearings. According to the second embodiment, a configuration of the pump is adopted taking into consideration not only the external magnetic field in the radial direction but also the external magnetic field in the axial direction, so that the stability of the vacuum pump against the external magnetic field can be further increased.
The pump casing 2 and the thread stator 24 include magnetic materials having high permeability in the same manner as in the first embodiment. In the turbomolecular pump shown in FIG. 8, an electromagnet 38 a on an upper side in FIG. 8 that constitute the magnetic bearing 38 in the thrust direction is provided in the base 20. On the other hand, an electromagnet 38 b in a lower side in FIG. 8 is provided in the thrust covers 40 and 41 fastened to the bottom of the base 20. In the thrust covers 40 and 41, the axial displacement sensor 28 provided corresponding to the magnetic bearing 38 is also arranged. As mentioned above, the thrust covers 40 and 41 that are made of the magnetic material constitute a case for magnetic shielding in which the axial displacement sensor 28 and the lower electromagnet 38 b are housed.
FIG. 9 is a fragmentary view taken in the direction of arrow A in FIG. 8. At the inlet flange 21 b of the pump casing 2, a magnetic shield member 42 having a shape as shown in FIG. 9 is provided. The magnetic shield member 42 includes a disc portion 42 a that is disposed in the center of the inlet 21 a, a ring portion 42 b that is fastened to the inlet flange 21 b, and a connection portion 42 c. The connection portion 42 c functions as a beam for supporting the disc 42 a in the center of the inlet 21 a and at the same time functions as a magnetic path that conducts a magnetic flux from the disc portion 42 a to the ring portion 42 b. Four opening areas 421 surrounded by the disc portion 42 a, the ring portion 42 b, and the connection portion 42 c serve an actual opening of the pump. Here, it is assumed that the diameter size of the disc portion 42 a is D.
FIG. 10 is a diagram illustrating operations of the thrust covers 40 and 41 and the magnetic shield member 42 as magnetic shields. FIG. 10 shows a case in which an external magnetic field in the axial direction is applied to the pump body 1. The arrow lines denoted by reference numeral 300 represent magnetic fluxes. The magnetic fluxes, which enter the inlet flange 21 b from above in FIG. 10, apt to gather at a substance having high permeability, so that the magnetic fluxes are apt to gather at the magnetic shield member 42, which are made of the magnetic material, and the pump casing 2. As a result, the most portions of the magnetic fluxes 300 pass through the pump casing 2 to the base 20. Of course, since opening areas 420 are formed at the magnetic shield member 42, a portion of the magnetic fluxes enters the pump casing 2 via the opening areas 420.
As mentioned above, since the magnetic shield member 42 plays a role of a magnetic shield, it may be desirable to make the opening areas 421 smaller by increasing the diameter D of the disc portion 42 a, whereas to suppress a reduction in discharge performance of the vacuum pump, it may be desirable to make the opening areas 421 as large as possible. Thus, according to the present embodiment, with a view to decreasing the influence of the external magnetic field on the magnetic bearings, the diameter D of the disc portion 42 a is set so as to satisfy the following condition “Ds≦D≦Dri”. As shown in FIG. 8, Ds denotes an outer diameter of the radial displacement sensor 27, and Dri denotes a diameter of a circle that passes a joint portion of the rotary blade 32 at the uppermost stage.
The condition “D≦Dri” is set from the viewpoint of suppressing the reduction in discharge performance. Among the gas molecules that pass through the opening portion 420 of the magnetic shield member 42 and flow into the pump casing 2, those gas molecules that enter the pump casing 2 at a side more radially inward than the joint portion of the rotary blade 32 will bounce off on an upper surface of the rotor 30 to proceed toward the inlet side. That is, there is a low probability that the gas molecules flowing in after passing the central portion of the inlet 21 a are discharged by the pump. Therefore, if a disc portion 42 a that baffles flowing in of the gas molecules is disposed in the central portion of the inlet 21 a, the influence of it on the reduction in the performance of discharging can be held down. It is preferred that in order not to hinder the flow of the gas molecules that passes through the inlet 21 a and enters the pump at a side more radially outward than the joint portion of the rotary blade 32, the outer diameter D of the disc portion 42 a is not larger than the diameter Dri of the disc portion 42 a. From the viewpoint of a path for magnetic fluxes, it is preferred that the cross-sectional area of the connection portion 42 c is larger in order to avoid magnetic saturation. On the contrary, in order to prevent a decrease in the performance of discharging, it is preferred that the connection part 42 c has a smaller width W.
It should be noted that in the case of the magnetic shield member 42 shown in FIG. 9, it includes the ring part 42 b for attaching it to the inlet flange 2 lb. However, the connection part 42 c may be fastened to the inlet flange 21 b with the ring part 42 b being omitted.
On the other hand, the condition “DS≦D” is set in order to reduce the influence of the eternal magnetic field on the control of the magnetic bearing. The magnetic fluxes that enter through the opening portion 420 pass through the rotor 30 that is made of a non-magnetic material (for example, aluminum) to reach the magnetic bearing part. Then, in order to suppress the influence of the magnetic fluxes, the outer diameter D of the disc portion 42 a is set to be not smaller than the outer diameter Ds of the radial displacement sensor 27. With this setting, the magnetic fluxes that enter the pump casing 2 from the central portion of the inlet 21 a and reach the magnetic bearing portion are reduced.
The magnetic fluxes 300 that have passed through the pump casing 2 to the base 20 tend to gather at the thread stator 24 that is made of a magnetic material having relatively high permeability rather than passing straight downward through the base 20 that is made of an aluminum material. The magnetic fluxes 300 that have passed through the thread stator 24 flow though the thrust covers 40 and 41 fastened to the lower part of the base 20 via the base 20 to the outside of the pump. As a result, the components relating to the thrust magnetic bearing 38 are shielded by the thrust covers 40 and 41 and are not influenced by the external magnetic field. As mentioned above, the thrust covers 40 and 41 function as magnetic shield members that shield the influence by the external magnetic field and exhibit shielding effect not only against the external magnetic field in the axial direction but also the external magnetic field in the radial direction.
It should be noted that regarding the thrust cover 40, there is the possibility that it provides a path for the magnetic flux of the electromagnet 38 b. Since generally the core of the electromagnet 38 b includes pure steel or the like having high permeability, the influence of the thrust cover 40 is not considered to be so strong, however, it is necessary to take care in selecting magnetic materials. For this reason, it is preferred to select a material for the thrust cover 40 such that it has permeability that is lower than the permeability of the core.
Since no particularly high strength is necessary for the thrust covers 40 and 41 and the magnetic shield member 42, it is possible to select materials having high saturated magnetic flux density from among the magnetic materials shown in FIGS. 4 and 5. For example, in the case of carbon steels, saturated magnetic flux density is higher as the carbon content is lower. Accordingly, in the case of the material shown in FIG. 5, 510C shown in the uppermost column of the table is highest in the effect of magnetic shielding and becomes lower toward the bottom column. Since each of the thrust covers 40 and 41 and the magnetic shield member 42 is supposed to be disposed in a vacuum atmosphere, it is preferred that they are subjected to surface treatment for providing corrosion resistance, such as Ni—P plating, electrodeposition or the like.
FIG. 11 presents a diagram that shows a variation example of the turbomolecular pump shown in FIG. 8. In this variation example, the thrust cover 40 is additionally provided with a disc 40 b and a cylinder 40 c that are made of a magnetic material. The thrust cover 40 and the disc 40 b, or the disc 40 b and the cylinder 40 c may be fastened with bolts and the like. Alternatively, the thrust cover 40, the disc 40 b, and the cylinder 40 c may be formed as one body. It should be noted that when the disc 40 b and the cylinder 40 c are formed separately from the thrust cover 40, the surface treatment such as Ni—P plating on the disc 40 b and the cylinder 40 c may be omitted.
The construction shown in FIG. 10 is configured such that the magnetic fluxes that have passed through the pump casing 2 are guided toward the thrust cover 40 via the thread stator 24. However, in case that it is difficult for the thread stator 24, which serves as a path for the magnetic fluxes, to have a relatively large cross-sectional area because of its design, it may happen that the intensity of the external magnetic field exceeds the saturated magnetic flux density of the thread stator 24 at some intensity or higher. In such a case, there is the possibility that the magnetism leaks out and eddy current is generated in the cylindrical portion 31 of the rotor 30 which is in close vicinity thereto.
Accordingly, in the variation examination shown in FIG. 11, the disc 40 b and the cylinder 40 c that are made of a magnetic material are provided so as to extend from the thrust cover 40 in the direction of the fastened flange 21 c of the pump casing 2. With such a structure, the magnetic fluxes enter the cylindrical portion 40 c from the pump casing and pass through the disc 40 b and the thrust covers 40 and 41 to come out downward. In this case, the thread stator 24 may be made of either a magnetic material or a non-magnetic material.
In the magnetic shield member 42 according to the second embodiment presents an example of the magnetic shield member disposed at the inlet 21 a and may have the shape shown in FIG. 12. In FIG. 12, a plurality of circular opening areas 422 having an area smaller than that of the opening 421 shown in FIG. 9 are uniformly distributed in the inlet region. The diameter of the circular opening areas 422 may be made smaller to have the function of the conventional protective net simultaneously.
The embodiments may be used singly or combined with each other. This is because the effects of the embodiments can be exhibited singly or in synergism. For example, depending on the environment in which the pump is used, all of the pump casing 2, the thread stator 24, the magnetic shield member 42, the thrust covers 40 and 41, the disc 40 a, and the cylinder 40 b may be implemented or some of them may be selectively implemented.
The present invention may be applied similarly to a vacuum pump with only a turbomolecular pump unit and a vacuum pump with only a drag pump unit.
Although in the above description, various embodiments and variation examples have been explained, the present invention is not limited thereto. Other embodiments that are conceivable within the scope of the technical concept of the present invention are contained in the scope of the present invention.
The disclosures of the following base applications to which priority is claimed in the present application are incorporated herein by reference:
Japanese Patent Application No. 2010-177136 (filed Aug. 6, 2010), and
Japanese Patent Application No. 2010-232977 (filed Oct. 15, 2010).

Claims

1. A vacuum pump comprising:

a rotor provided with a rotor-side discharge function unit;

a motor that drives the rotor to rotate with respect to a stator-side discharge function unit; and

a cylindrical pump casing made of a magnetic material, in which the rotor and the stator-side discharge function unit are disposed.

2. A vacuum pump according to claim 1, wherein

the rotor-side discharge function unit includes

a plurality of stages consisting of rotor turbine blades disposed in an inner space of the pump casing, and

a cylindrical drag pump rotating portion provided at a downstream side of the stages consisting of rotor turbine blades outside the inner space of the pumping casing, and

the stator-side discharge function unit includes

a plurality of stages consisting of stator turbine blades, and

a cylindrical drag pump fixing portion which is disposed so as to surround an outer circumferential surface of the drag pump rotating portion at a gap therefrom and which is made of a magnetic material.

3. A vacuum pump according to claim 1, further comprising:

a magnetic bearing unit that includes a thrust magnetic bearing that supports the rotor in an axial direction and a radial bearing that supports the rotor in a radial direction,

a pump base portion that is provided with the magnetic bearing unit and that is made of a non-magnetic material,

an axial sensor that detects a position in the axial direction of the rotor,

a radial sensor that detects a position in the radial direction of the rotor,

a first magnetic shield member that is made of a magnetic material and that is provided at an inlet of the pump casing to reduce entrance of external magnetic field into the pump via the inlet, and

a second magnetic shield member that is made of a magnetic material and that is provided at the pump base portion to reduce influence of external magnetic field on the magnetic bearing unit.

4. A vacuum pump according to claim 3, wherein

the second magnetic shield member constitutes a vacuum container in which at least the axial sensor is housed.

5. A vacuum pump according to claim 4, further comprising:

a third magnetic shield member made of a magnetic material that extends in the direction of from the second magnetic shield member to the pump casing so as to cover an outer circumferential surface of the pump base portion that is made of the non-magnetic material.

6. A vacuum pump according to claim 5, wherein

the second magnetic shield member and the third magnetic shield member are formed into a one body

7. A vacuum pump according to claim 3, wherein

the magnetic shield member includes a disc portion and a supporting beam that supports the disc portion at a center of the inlet.

8. A vacuum pump according to claim 7, wherein

the rotor includes a plurality of stages consisting of turbine blades as the rotor-side discharge function unit,

the disc portion has an outer diameter D, which is not smaller than an outer diameter Ds of the radial sensor and not larger than a diameter Dri of a circle that passes a joint of each of the turbine blades in a circumferential direction of the rotor.

9. A vacuum pump according to claim 1, further comprising:

a protective net that is fastened to the inlet of the pump casing with bolts to prevent foreign matter from entering the pump, the pump casing being formed of threaded through-holes for fastening with bolts.

10. A vacuum pump according to claim 3, wherein

the first magnetic shield member serves as the protective net that is provided at the inlet of the pump casing and prevents foreign matter from entering the pump.

11. A vacuum pump according to claim 1, wherein

the magnetic material includes a carbon steel or an alloy steel.

12. A vacuum pump according to claim 11, wherein

the pump casing is made of S45C as the carbon steel.

13. A vacuum pump according to claim 11, wherein

a surface of the magnetic material is subjected to anticorrosion treatment including N—P plating treatment.