Vacuum pump and method for determining shape of roots rotors

Abstract

To provide a vacuum pump in which powder is hardly sandwiched between Roots rotors, and that can keep smooth rotation of the Roots rotors.SOLUTION: A first Roots rotor 8 and a second Roots rotor 9 each comprise involute side surfaces 31 each having a shape formed of an involute curve, arc convex surfaces 34 connected to outside end parts of the involute side surfaces 31, and arc concave surfaces 36 connected to inside end parts of the involute side surfaces 31. A curvature radius R1 of the arc convex surfaces 34 is smaller than a curvature radius R2 of the arc concave surfaces 36.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a vacuum pump, and more particularly to a vacuum pump suitable for use in exhausting process gases used in the manufacture of semiconductor devices, liquid crystal panels, LEDs, solar cells, and the like. [Background technology]

[0002] In manufacturing processes for manufacturing semiconductor devices, liquid crystal panels, LEDs, solar cells, etc., process gas is introduced into a process chamber to perform various processes such as etching and CVD. The process gas introduced into the process chamber is exhausted by a vacuum pump. In general, the vacuum pumps used in these manufacturing processes, which require high cleanliness, are so-called dry vacuum pumps that do not use oil in the gas flow path. A typical example of such a dry vacuum pump is a positive displacement vacuum pump that transfers gas by rotating a pair of Roots rotors arranged in a rotor chamber in opposite directions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 1-077782 Summary of the Invention [Problem to be solved by the invention]

[0004] The process gas may contain powder consisting of by-products. Such powder flows into the vacuum pump together with the process gas. Also, depending on the conditions inside the vacuum pump (e.g., temperature, pressure), powder may be generated inside the vacuum pump after the process gas flows into the vacuum pump. Most of the powder is discharged from the vacuum pump together with the process gas, but some of the powder remains in the rotor chamber and gradually accumulates in the rotor chamber. In particular, when the convex and concave surfaces of two opposing Roots rotors are in surface contact (actually non-contact), the powder has no place to escape, and the powder is tightly pinched between the convex and concave surfaces of the Roots rotors, which may hinder the rotation of the Roots rotors.

[0005] Therefore, the present invention provides a vacuum pump that is less likely to trap powder in the roots rotor and can maintain smooth rotation of the roots rotor. The present invention also provides a method for determining the shape of such a roots rotor. [Means for solving the problem]

[0006] In one aspect, a vacuum pump is provided, comprising a pump casing having at least one rotor chamber therein, and a first roots rotor and a second roots rotor arranged in parallel within the rotor chamber, each of the first roots rotor and the second roots rotor having an involute side surface having a shape formed by an involute curve, an arc convex surface connected to an outer end of the involute side surface, and an arc concave surface connected to an inner end of the involute side surface, wherein the radius of curvature of the arc convex surface is smaller than the radius of curvature of the arc concave surface.

[0007] In one aspect, each of the arcuate convex surface and the arcuate concave surface is longer than the involute side surface. In one aspect, when the arcuate convex surface and the arcuate concave surface face each other, the width of the space formed between the arcuate convex surface and the arcuate concave surface increases with increasing distance from the position of the minimum gap between the arcuate convex surface and the arcuate concave surface. In one embodiment, the radius of curvature of the arcuate convex surface is 0.2 to 0.9 times the radius of curvature of the arcuate concave surface.

[0008] In one aspect, a method for determining a shape of a Roots rotor is defined, the method including: generating, by the calculation system, a plurality of candidates for Roots rotors having a shape that satisfies a Roots rotor specification while changing the specifications; calculating, by the calculation system, a plurality of gaps between a pair of Roots rotors corresponding to a plurality of rotation angles of the pair of Roots rotors having a shape of one of the plurality of candidates; determining a maximum gap among the plurality of gaps; repeating the calculation of the plurality of gaps and the determination of the maximum gap for the plurality of candidates to determine a plurality of maximum gaps corresponding to the plurality of candidates; and determining a candidate Roots rotor shape corresponding to the smallest maximum gap among the plurality of maximum gaps.

[0009] In one aspect, the method further includes calculating additional gaps corresponding to additional rotation angles by interpolating the plurality of gaps corresponding to the plurality of rotation angles, and the maximum gap is determined from the plurality of gaps and the additional plurality of gaps. In one aspect, the Roots rotor has an involute side surface having a shape consisting of an involute curve, an arc convex surface connected to an outer end of the involute side surface, and an arc concave surface connected to an inner end of the involute side surface, and the radius of curvature of the arc convex surface is smaller than the radius of curvature of the arc concave surface. In one aspect, the specifications of the root rotor include at least one of the center distance of a pair of root rotors, the pressure angle of the involute side of the root rotors, the radius of the root rotors, the gap between the root rotors, the radius of curvature of the arc-shaped convex surface of the root rotors, and the radius of curvature of the arc-shaped concave surface of the root rotors. Effect of the Invention

[0010] The radius of curvature of the arc convex surface of the first roots rotor is smaller than that of the arc concave surface of the second roots rotor, so a point on the arc convex surface of the first roots rotor and a point on the arc concave surface of the second roots rotor form a minimum gap, and the gap between the roots rotors gradually widens on both sides of the minimum gap. Therefore, the powder is less likely to be pinched between the arc convex surface of the first roots rotor and the arc concave surface of the second roots rotor. As a result, the roots rotor can maintain smooth rotation. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating an embodiment of a vacuum pump apparatus. [Diagram 2] 2 is a cross-sectional view taken along line AA in FIG. 1. [Diagram 3] FIG. 2 is an enlarged view of the Roots rotor. [Figure 4] FIG. 4 is an enlarged view illustrating the gap between the root rotors. [Diagram 5] FIG. 1 shows two Roots rotors rotating in opposite directions. [Figure 6] FIG. 1 is a schematic diagram illustrating an embodiment of a computing system for determining a Roots rotor shape. [Figure 7] 1 is a flow chart illustrating an embodiment of a method for determining a shape of a Roots rotor. [Figure 8] 1 is a graph showing a change in the gap between a pair of Roots rotors when the Roots rotors are rotated once. [Figure 9] FIG. 1 illustrates an embodiment of a three-lobe Roots rotor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of a vacuum pump device, and FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. The vacuum pump device of the embodiment described below is a positive displacement vacuum pump device. In particular, the vacuum pump device shown in FIG. 1 and FIG. 2 is a so-called dry vacuum pump device that does not use oil in a gas flow path. Since vaporized oil does not flow upstream, the dry vacuum pump device can be suitably used in semiconductor device manufacturing equipment that requires high cleanliness.

[0013] As shown in Fig. 1, the vacuum pump apparatus includes a vacuum pump 1 and an electric motor 2 that drives the vacuum pump 1. The vacuum pump 1 in this embodiment is a single-stage vacuum pump. That is, the vacuum pump 1 includes a pump casing 6 having a rotor chamber 5 therein, single-stage Roots rotors 8, 9 arranged in the rotor chamber 5, and a pair of rotating shafts 11, 12 that support the Roots rotors 8, 9. In one embodiment, the vacuum pump 1 may be a multi-stage vacuum pump having multiple Roots rotors arranged in multiple rotor chambers.

[0014] Although only the Roots rotor 8 and the rotating shaft 11 are shown in Fig. 1, the Roots rotor 8 and the Roots rotor 9 are arranged in parallel inside the pump casing 6, and the rotating shaft 11 and the rotating shaft 12 are arranged in parallel. Fig. 2 shows the Roots rotor 8 and the Roots rotor 9 arranged in parallel to each other. The Roots rotor 8 is supported by the rotating shaft 11, and the Roots rotor 9 is supported by the rotating shaft 12.

[0015] The Roots rotors 8 and 9 are not in contact with each other, and are not in contact with the inner surface of the pump casing 6. Therefore, the Roots rotors 8 and 9 can rotate smoothly within the pump casing 6 without the use of lubricating oil.

[0016] The Roots rotor 8 and the rotating shaft 11 may be an integral structure. Similarly, the Roots rotor 9 and the rotating shaft 12 may be an integral structure. The electric motor 2 is coupled to one of the rotating shafts 11, 12. In one embodiment, a pair of electric motors 2 may be coupled to the rotating shafts 11, 12, respectively.

[0017] The pump casing 6 has a gas inlet 14 and a gas outlet 15 that communicate with the rotor chamber 5. The gas inlet 14 is connected to a chamber (not shown) filled with a gas to be transported. In one example, the gas inlet 14 is connected to a process chamber of a semiconductor device manufacturing apparatus, and the vacuum pump 1 is used to exhaust a process gas introduced into the process chamber.

[0018] The vacuum pump 1 further includes a gear housing 16 located outside the side wall 6A of the pump casing 6. A pair of gears 20 that mesh with each other are arranged inside the gear housing 16. Note that only one gear 20 is illustrated in FIG. 1. These gears 20 are fixed to the rotating shafts 11 and 12, respectively. The electric motor 2 is rotated by a motor driver (not shown), and one of the rotating shafts 11 and 12 to which the electric motor 2 is connected rotates the other of the rotating shafts 11 and 12 to which the electric motor 2 is not connected in the opposite direction via the gear 20.

[0019] The rotating shafts 11, 12 are rotatably supported by a bearing 17 held in the side wall 6A of the pump casing 6 and a bearing 18 held in the other side wall 6B of the pump casing 6. The electric motor 2 has a motor housing 22 located outside the side wall 6B of the pump casing 6, and a motor rotor 2A and a motor stator 2B arranged within the motor housing 22.

[0020] In one embodiment, a pair of electric motors 2 may be provided, each connected to the rotating shafts 11, 12. The pair of electric motors 2 are rotated in synchronous opposite directions by a motor driver (not shown), and rotate the rotating shafts 11, 12 and the roots rotors 8, 9 in synchronous opposite directions as shown in Fig. 2. In this case, the role of the gear 20 is to prevent the synchronous rotation of the roots rotor 8 from being lost due to an unexpected external factor.

[0021] As the electric motor 2 rotates the Roots rotors 8, 9, gas is drawn into the rotor chamber 5 through the gas inlet 14. The gas is delivered to the gas outlet 15E by the rotation of the Roots rotors 8, 9 within the rotor chamber 5 and is discharged from the pump casing 6 through the gas outlet 15E.

[0022] The Roots rotors 8 and 9 have the same outer shape. Therefore, the Roots rotor 8 will be described below. FIG. 3 is an enlarged view of the Roots rotor 8. As shown in FIG. 3, the Roots rotor 8 has an involute side surface 31 having a shape formed by an involute curve, an arc convex surface 34 connected to the outer end of the involute side surface 31, and an arc concave surface 36 connected to the inner end of the involute side surface 31. The Roots rotor 8 is a so-called two-lobe Roots rotor having two protrusions. Therefore, the Roots rotor 8 has two arc convex surfaces 34, four involute side surfaces 31, and two arc concave surfaces 36. The two arc convex surfaces 34 are connected to the outer ends of the four involute side surfaces 31, and the two arc concave surfaces 36 are connected to the inner ends of the four involute side surfaces 31. Each of the arc convex surfaces 34 and the arc concave surfaces 36 is longer than the involute side surface 31.

[0023] The radius of curvature R1 of the arcuate convex surface 34 is smaller than the radius of curvature R2 of the arcuate concave surface 36. In one embodiment, the radius of curvature R1 of the arcuate convex surface 34 is 0.2 to 0.9 times the radius of curvature R2 of the arcuate concave surface 36. Therefore, as shown in FIG. 4, when the arcuate convex surface 34 of the roots rotor 8 faces the arcuate concave surface 36 of the roots rotor 9, only one point on the arcuate convex surface 34 of the roots rotor 8 and one point on the arcuate concave surface 36 of the roots rotor 9 are close to each other, and a minimum gap G1min is formed between the arcuate convex surface 34 and the arcuate concave surface 36. The width W of the space 40 gradually increases with increasing distance from the position where the minimum gap G1min is formed.

[0024] Since the radius of curvature R1 of the arcuate convex surface 34 of the roots rotor 8 is smaller than the radius of curvature R2 of the arcuate concave surface 36 of the roots rotor 9, one point on the arcuate convex surface 34 of the roots rotor 8 and one point on the arcuate concave surface 36 of the roots rotor 9 form a minimum gap G1min, and the gap between the roots rotors 8 and 9 gradually widens on both sides of the minimum gap G1min. Therefore, the powder is less likely to be pinched between the arcuate convex surface 34 of the roots rotor 8 and the arcuate concave surface 36 of the roots rotor 9. As a result, the roots rotors 8 and 9 can maintain smooth rotation.

[0025] FIG. 5 is a diagram showing two root rotors 8 and 9 rotating in opposite directions. As shown in FIG. 5, the involute side surfaces 31 of the root rotor 8 and the root rotor 9 face each other, and do not face the arc convex surface 34 and the arc concave surface 36. On the other hand, the arc convex surface 34 of the root rotor 8 faces the arc concave surface 36 of the root rotor 9, and does not face the involute side surface 31 of the root rotor 9. Similarly, the arc convex surface 34 of the root rotor 9 faces the arc concave surface 36 of the root rotor 8, and does not face the involute side surface 31 of the root rotor 8. While the root rotor 8 and the root rotor 9 rotate once, the root rotor 8 and the root rotor 9 do not make line contact, but make point contact (actually non-contact). Therefore, powder is unlikely to be caught between the root rotor 8 and the root rotor 9. The gap G2 between the involute side surfaces 31 of the two root rotors 8 and 9 is always constant.

[0026] The involute side surface 31 is an outwardly curved surface. Therefore, a gap G2 is formed between one point on the involute side surface 31 of the Roots rotor 8 and one point on the involute side surface 31 of the Roots rotor 9, and the gap widens on both sides of the gap G2. Due to such point contact of the involute side surface 31 (actually non-contact), powder is unlikely to get caught between the involute side surface 31 of the Roots rotor 8 and the involute side surface 31 of the Roots rotor 9.

[0027] Next, a method for determining the shapes of the above-mentioned Roots rotors 8, 9 will be described. The shapes of the Roots rotors 8, 9 are determined by a calculation system 50 shown in FIG. 6. The calculation system 50 includes a storage device 50a in which a program is stored, and a processing device 50b that executes calculations according to instructions included in the program. The calculation system 50 is composed of at least one computer. The storage device 50a includes a main storage device such as a random access memory (RAM), and an auxiliary storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Examples of the processing device 50b include a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit). However, the specific configuration of the calculation system 50 is not limited to these examples.

[0028] FIG. 7 is a flow chart illustrating one embodiment of a method for determining a Roots rotor shape. In step 1, the calculation system 50 generates multiple candidates for a root rotor having a shape that satisfies the specifications while changing the specifications of the root rotor. The specifications of the root rotor include at least one of the center distance of a pair of root rotors, the pressure angle of the involute side surface 31 of the root rotor, the radius of the root rotor, the gap between the root rotors, the curvature radius of the arc convex surface 34 of the root rotor, and the curvature radius of the arc concave surface 36 of the root rotor. The calculation system 50 generates multiple candidates for a root rotor having a shape that satisfies the specifications while changing at least one of these elements (conditions) that constitute the specifications. For example, the calculation system 50 generates multiple candidates for a root rotor having a shape that satisfies the specifications while changing the pressure angle of the involute side surface 31 of the root rotor, the curvature radius of the arc convex surface 34 of the root rotor, and the curvature radius of the arc concave surface 36 of the root rotor.

[0029] In step 2, the calculation system 50 calculates a plurality of gaps between a pair of Roots rotors having a shape of one of the plurality of candidates, which correspond to a plurality of rotation angles of the pair of Roots rotors having the shape of each candidate. More specifically, the calculation system 50 calculates the gap between the Roots rotors at a predetermined rotation angle interval while rotating the pair of Roots rotors having each candidate shape in the opposite directions in the virtual space.

[0030] Fig. 8 is a graph showing the change in the gap between a pair of candidate Root rotors when they are rotated once. In Fig. 8, the vertical axis represents the gap between the Root rotors, and the horizontal axis represents the rotation angle of the Root rotors. When the involute side surfaces 31 of the two Root rotors face each other, the gap G2 between the Root rotors is approximately constant, but when the arc convex surface 34 and the arc concave surface 36 of the two Root rotors face each other, the gap G1 between the Root rotors changes.

[0031] The calculation system 50 calculates the gap between the Roots rotors at each rotation angle. Thus, multiple gaps corresponding to multiple rotation angles are obtained. The calculation system 50 determines the maximum gap among the multiple obtained gaps. In the example of FIG. 8, the maximum gap is the peak value of the graph. If the maximum gap is too large, the exhaust performance of the vacuum pump 1 will decrease.

[0032] Depending on the shape of the Roots rotors, the calculated gap between the Roots rotors at a certain rotation angle may be negative. A negative gap means that the Roots rotors are touching. When the Roots rotors are touching, the rotation of the Roots rotors is inhibited. Therefore, in step 3, the calculation system 50 determines whether there is a negative gap among the multiple gaps calculated in step 2 above. In step 4, if there is a negative gap, the calculation system 50 removes the candidate with the negative gap from the plurality of candidates generated in step 1 above.

[0033] In step 5, the computing system 50 determines the maximum gap from among the gaps calculated for each candidate. In step 6, the calculation system 50 repeats the calculation of the gaps and the determination of the maximum gap for the candidates to determine the maximum gaps corresponding to the candidates, respectively. More specifically, the calculation system 50 repeats steps 2 to 5. In step 7, the computing system 50 determines a candidate Roots rotor shape that corresponds to the smallest maximum gap among the multiple maximum gaps determined in step 6 above. In this manner, the shapes of the Roots rotors 8 and 9 described with reference to FIGS. 1 to 5 are determined.

[0034] In one embodiment, in step 2, in order to calculate the gap between the Roots rotors at finer rotation angle intervals, the calculation system 50 may calculate additional gaps by interpolating the calculated gaps along the rotation angle. That is, the calculation system 50 interpolates additional gaps corresponding to additional rotation angles. An example of the interpolation is spline interpolation. In step 5, the maximum gap is determined from among the gaps calculated in step 2 and the additional gaps.

[0035] The gap interpolation may be performed only within a predetermined rotation angle range. For example, the gap interpolation may be performed within a rotation angle range in which the arc convex surface 34 and the arc concave surface 36 face each other, as shown in Fig. 4. In particular, the gap interpolation may be performed within a rotation angle range including a rotation angle at which the gap G1 between the arc convex surface 34 and the arc concave surface 36 is smallest (the rotation angle of the bottom point between the two peak points in Fig. 8).

[0036] The roots rotors 8 and 9 in the above-described embodiments are two-lobe roots rotors having two lobes, but the present invention is not limited to the above-described embodiments and can also be applied to three-lobe roots rotors having three lobes, or multi-lobe roots rotors having four or more lobes.

[0037] For example, Fig. 9 is a diagram showing an embodiment of a three-lobe root rotor. In this embodiment, each of the root rotors 51, 52 has an involute side surface 31 having a shape formed by an involute curve, an arc convex surface 34 connected to an outer end of the involute side surface 31, and an arc concave surface 36 connected to an inner end of the involute side surface 31, and the radius of curvature R3 of the arc convex surface 34 is smaller than the radius of curvature R4 of the arc concave surface 36. The configuration of the three-lobe root rotors 51, 52 in this embodiment that is not particularly described is the same as that of the above embodiment described with reference to Figs. 1 to 5, so that the overlapping description will be omitted.

[0038] The embodiment of the method for determining the shape of a Roots rotor described with reference to Figures 6 to 8 can also be applied to a three-lobe Roots rotor, as shown in Figure 9, and to a multi-lobe Roots rotor having four or more lobes.

[0039] The above-described embodiments have been described for the purpose of enabling a person having ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments are naturally possible for a person skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope according to the technical idea defined by the claims. [Explanation of symbols]

[0040] 1. Vacuum pump 2 electric motor 2A motor rotor 2B Motor stator 5 Rotor Room 6 Pump casing 8,9 Roots Rotor 11,12 Rotation axis 14 Gas inlet 15 Gas outlet 16 Gear housing 17 Bearings 18 Bearings 20 Gear 22 Motor housing 31 Involute side 34 Convex arc 36 Concave Arc 40 space 50 Computing Systems

Claims

1. a pump casing having at least one rotor chamber therein; a first Roots rotor and a second Roots rotor arranged in parallel in the rotor chamber; each of the first root rotor and the second root rotor has an involute side surface having a shape formed by an involute curve, an arc convex surface connected to an outer end of the involute side surface, and an arc concave surface connected to an inner end of the involute side surface; A vacuum pump, wherein the radius of curvature of the convex arc surface is smaller than the radius of curvature of the concave arc surface.

2. The vacuum pump of claim 1 , wherein each of the arcuate convex surface and the arcuate concave surface is longer than the involute side surface.

3. 2. The vacuum pump according to claim 1, wherein when the arcuate convex surface and the arcuate concave surface face each other, a width of a space formed between the arcuate convex surface and the arcuate concave surface increases with increasing distance from a position of a minimum gap between the arcuate convex surface and the arcuate concave surface.

4. 2. The vacuum pump according to claim 1, wherein the radius of curvature of the arcuate convex surface is 0.2 to 0.9 times the radius of curvature of the arcuate concave surface.

5. 1. A method for determining a roots rotor shape, comprising: By changing the specifications of the Roots rotor, a calculation system generates multiple candidates of the Roots rotor having a shape that satisfies the specifications, calculating, by the calculation system, a plurality of gaps between the pair of Roots rotors corresponding to a plurality of rotation angles of the pair of Roots rotors having one of the plurality of candidate shapes; determining a maximum gap among the plurality of gaps; Repeating the calculation of the plurality of gaps and the determination of the maximum gap for the plurality of candidates to determine a plurality of maximum gaps corresponding to the plurality of candidates; determining a candidate Roots rotor shape corresponding to a smallest maximum clearance among the plurality of maximum clearances.

6. and calculating additional gaps corresponding to additional rotation angles by interpolating the gaps corresponding to the rotation angles; The method of claim 5 , wherein the maximum gap is determined from the plurality of gaps and the additional plurality of gaps.

7. 6. The method of claim 5, wherein the determined shape of the Roots rotors is the first Roots rotor and the second Roots rotor of any one of claims 1 to 3.

8. 8. The method according to claim 7, wherein the specifications of the Root rotor include at least one of a center distance between a pair of Root rotors, a pressure angle of the involute side surface of the Root rotor, a radius of the Root rotor, a gap between the Root rotors, a radius of curvature of the convex arc surface of the Root rotor, and a radius of curvature of the concave arc surface of the Root rotor.

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