JPH0765592B2 - Turbo molecular pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a turbo-molecular pump that gives gas molecules momentum in a specific direction for exhausting the gas.

[Conventional technology]

FIG. 8 shows an example of a conventional turbo molecular pump.
In the figure, reference numeral 1 denotes a rotary blade provided on a peripheral surface of a rotary impeller 2, and a fixed blade 4 fixed to an inner surface of a cylindrical case 3.
It is provided corresponding to. A large number of rotary blades 1 and fixed blades 4 are alternately arranged, and a turbo function is formed by the relative high speed rotation of both of them to give a momentum in a specific direction to gas molecules. The intake port 5 is provided above the array, and the exhaust port 6 is provided below the intake port 5.

The rotary impeller 2 includes a motor 7 that is erected from the inner bottom of the case 3.
Is fixed to one end of the drive shaft 8. The motor 7 is generally of an outer rotor type in which a rotor magnet is fixed to a drive shaft 8.

FIG. 9 partially shows the rotary blade 1 provided on the peripheral surface of the rotary impeller 2 and the fixed blade 4 fixed to the inner surface of the case 3. The rotary vanes 1 and the fixed vanes 4 are obliquely arranged on the peripheral surface of the rotary vane wheel 2 and the inner surface of the case 3, and the momentum from the intake port 5 to the exhaust port 6 (from upper to lower in FIG. 9). Is given to the gas molecule. The axis of the rotary shaft 8 And the wing face vector Then the face vector The angle α formed by and is increased on the intake port 5 side and decreased on the exhaust port 6 side to improve efficiency. If the center position of the blade surfaces of the rotary blade 1 and the fixed blade 4 is r, the surface vector The angle φ (see FIG. 10) formed with respect to was π / 2.

[Problems to be solved by the invention]

In the conventional turbo molecular pump, since (φ = π / 2), the molecules reflected on the blade surface are repelled in the tangential direction of the rotating cylindrical surface of the blade on average. Therefore, the molecules collide with the outside of the center of the blade surface of the next stage, and the blade is not used effectively. Further, when (α> 20 °), there was a problem that the efficiency of the pump was difficult to improve even if the rotation speed was increased.

Therefore, an object of the present invention is to provide a turbo-molecular pump having an improved exhaust function on the blade surface of a rotary blade or a fixed blade.

[Means for solving problems]

In this invention, in a turbo molecular pump in which a rotating blade is rotated at a high speed with respect to a fixed blade to give momentum in a specific direction to a molecule, the rotor is rotated on the peripheral surface of a rotating impeller whose outer diameter is substantially constant in the axial direction. At least one of the rotor blades and the fixed blades is provided in a cylindrical coordinate system in which the blades are provided, the axial direction of the rotor wheel is Z, and the center position of the blade surfaces of the rotor blades and the fixed blades is r. Let α be the angle formed by the surface vectors A and Z of r, and (π-φ) be the angle formed by r and A. Let α be the angle φ of (φ <(π / 2)) and α be the blade pitch Lz. Accordingly, the direction of the molecules reflected on the blade surface is oriented toward the center side of the blade surface of the next stage or the next stage on average, by adaptively determining.

[Action]

The molecules reflected on the blade surface collide not with the outside of the blade surface of the next stage or the next stage but with the center on the average. The flow of molecules in the turbo molecular pump concentrates at the center of the blade surface, and the number of molecules that pass through the gap between the outside and the inside of the blade is reduced, so that the function of the blade is improved.

〔Example〕

 An embodiment of the present invention will be described below.

An example of this is where the reflection of molecules on the wing surface follows the cosine law.

In this embodiment, the angle φ is determined so that the molecules reflected on the blade surface collide with the center of the blade of the next stage or the next stage at the average. As shown in Fig. 1, the position vector of the center of the wing surface And wing face vector The angle formed by is (π-φ), but before determining this angle φ, Determine the angle φ ′ seen from.

In FIG. 2A, A1 is a surface vector The projection component on the plane orthogonal to is shown. A two-dot chain line 11 in FIG. 2A indicates a locus drawn by the rotor and the center of the rotor, and the rotor has a velocity v in the tangential direction. Also,
In FIG. 2B, A2 is a surface vector The projection component on the plane orthogonal to is shown. FIG. 2B shows 3 shows a rotary blade having a multi-stage configuration and a continuous three-stage portion of the rotary blade. In FIG. 2B, the alternate long and short dash line
12, 13 and 14 show the loci of the centers of the blade surfaces. The surface vector of each wing surface is To be mounted at an angle of α equal to, and the tilts are alternately reversed, and in FIG. 2B,
Momentum in the direction from top to bottom is given to the molecule. Also, Lz is the pitch of the blade, that is, the center of the rotor and the fixed blade. Is the interval.

The essential parts of FIGS. 2A and 2B are enlarged and shown in FIGS. 3A and 3B, respectively. In FIGS. 2 and 3, the molecule reflected at the point P must point to the point Q on the locus of the center of the next-stage blade surface. Therefore, If the angle formed by is (π−φ ′), There are the following relationships.

2rcosφ′sinφ ′ ＝ Lztanα That is, sin2φ ′ ＝ (Lz / r) tanα Moreover, the relation between φ and φ ′ is given by tanφ ＝ tanφ ′ / sinα from Fig. 3, and if r, Lz, α are given, φ is determined. Young
When giving φ smaller than (π / 2) to only one of the rotary blade or the fixed blade, the pitch should be doubled to 2Lz.

Next, a fourth example of a method of actually giving the angle φ obtained as described above to the rotary blade and / or the fixed blade
It is shown in FIGS. 4A and 4B show the structure of a rotary blade, and FIGS. 5A and 5B show the structure of a fixed blade. 4A and 5A show The shape of the wing viewed from is shown by hatching, and FIGS. 4B and 5B show The shape of the wing viewed from is shown by hatching. The thickness of the blade is 0, the radial length of the blade is d, and Was set to b. Further, in FIG. 4, reference numeral 15 indicates the outer peripheral surface of the rotary impeller to which the rotary blades are attached, and in FIG. 5, 16 indicates the inner peripheral surface of the case to which the fixed blades are attached.

Wings are at (φ = π / 2) Tilt the angle of the side of The projection on the plane orthogonal to is (π−φ ′). If this is a rotary wing, the fixed wing will tilt opposite to the rotary wing.

As an example, if (r = 25 cm, Lz = 4 cm, α = 15 °), then (φ ′ = 88.77 °, φ = 89.68 °) is set. If φ is given only to the fixed wing, (r = 25cm, α = 35
)), Even with the same pitch as the above example, Lz is doubled, so (Lz = 8cm), and (φ ′ = 83.53 °, φ = 8
6.28 °).

FIG. 6 and FIG. 7 show another example of a method of giving an angle of φ to the rotary blade and the fixed blade. 6A and 6B
Shows the rotor blades (hatched) From the shape and rotor seen from The respective shapes as viewed from are shown. 7A and 7B show fixed blades (shown by hatching). The shape and fixed wing seen from The respective shapes as viewed from are shown. As is clear from FIGS. 6 and 7, by pushing down the tip of the wing attached at an angle α, the plane vector of the wing surface can be reduced. The projection onto the plane orthogonal to is (π−φ ′). The mounting method shown in FIGS. 6 and 7 is Is larger than the width b in FIGS. 4 and 5, as indicated by b '.

Further, in the above description, it is assumed that the reflection of molecules on the blade surface follows the cosine law. However, the angle of incidence of molecules on the wing surface,
It is known that there is a deviation from the cosine law depending on the type of molecule. As the number of rotations increases, the incident angle of molecules tends to decrease, and mirror reflection tends to occur. Therefore, not only the angle φ is determined by the above theoretical formula, but the optimum angle φ may be determined experimentally.

〔The invention's effect〕

According to this invention, the flow of molecules in the turbo molecular pump is gathered at the center of the blade, and the gap existing between the tip of the rotary blade and the inner peripheral surface of the case or the tip of the fixed blade and the outer circumference of the rotary impeller. Molecules that slip through the gaps existing between the faces can be reduced, and the function of the blade can be improved. This result remarkably occurs when α is large and the degree of vacuum is high.

[Brief description of drawings]

FIG. 1 is a schematic diagram used for explaining an angle formed by a plane vector of a blade surface with a rotation axis, and FIGS. 2 and 3 are schematic diagrams used for explaining an angle formed by a plane vector and a rotation axis. FIGS. 4 and 5 are schematic diagrams used to describe an example of the shapes of the rotary blade and the fixed blade, and FIGS. 6 and 7 are schematic lines used to describe another example of the shapes of the rotary blade and the fixed blade. FIG. 8 is a cross-sectional view of an example of a conventional turbo molecular pump to which the present invention can be applied, and FIG. 9 is a schematic diagram used to describe a rotary blade and a fixed blade of a conventional turbo molecular pump, 10 The figure is a schematic diagram used for explaining an angle formed by a plane vector of a blade surface in a conventional turbo molecular pump with a rotation axis. Description of main symbols in the drawings

Claims (1)

[Claims] 1. A turbo-molecular pump in which a rotating blade is rotated at a high speed with respect to a fixed blade to give momentum in a specific direction to a molecule, and the outer diameter is substantially constant in the axial direction. Cylindrical coordinates in which the rotary vane is provided, the axial direction of the rotary vane is Z, and the center position of the vane surface of the rotary vane and the vane surface of the fixed vane is r.
When the angle between the surface vector A of at least one blade surface of the rotary blade and the fixed blade and Z is α, and the angle between r and A is (π−φ), (φ < (Π /
2)) The angle φ is adaptively determined according to α and the blade pitch Lz, so that the direction of the molecules reflected on the blade surface is on the center side of the blade surface at the next stage or the next stage in average. A turbo molecular pump aimed at.