Vacuum pump

Abstract

To provide a vacuum pump capable of preventing powder from being caught between roots rotors, maintaining smooth rotation of the roots rotors, and accurately measuring a clearance between the roots rotors by using a clearance gauge.SOLUTION: Each of the first Roots rotor 8 and the second Roots rotor 9 has an involute side surface 31 formed by an involute curve, an arc convex surface 34 located radially outward of the involute side surface 31, an arc concave surface 36 located radially inward of the involute side surface 31, an outer smooth curved surface 35 smoothly connecting the involute side surface 31 and the arc convex surface 34, and an inner smooth curved surface 37 smoothly connecting the involute side surface 31 and the arc concave surface 36. The curvature radius R1 of the arc convex surface 34 is smaller than the curvature radius R2 of the arc concave surface 36.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a vacuum pump, and more particularly to a vacuum pump that is 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 semiconductor devices, liquid crystal panels, LEDs, solar cells, and other products, process gases are introduced into process chambers for various processes such as etching and CVD. The process gases introduced into the process chamber are then exhausted using a vacuum pump. These manufacturing processes require high levels of cleanliness, and the vacuum pumps used are generally so-called dry vacuum pumps, which do not use oil in the gas flow path. A typical example of such a dry vacuum pump is a positive displacement vacuum pump, which transports gas by rotating a pair of Roots rotors in opposite directions inside a rotor chamber. [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] Process gases can contain powder by-products. These powders flow into the vacuum pump along with the process gas. Depending on the conditions inside the vacuum pump (e.g., temperature, pressure), powder may also be generated inside the vacuum pump after the process gas has entered the vacuum pump. While most of the powder is discharged from the vacuum pump along with the process gas, some of the powder remains in the rotor chamber and gradually accumulates there. In particular, when the convex and concave surfaces of two opposing Roots rotors are in surface contact (actually non-contact), the powder has no way to escape and can become tightly trapped between the convex and concave surfaces of the Roots rotors, hindering the rotation of the Roots rotors.

[0005] On the other hand, to improve pump efficiency, it is desirable to minimize the gap between the Roots rotors. Therefore, after the Roots rotors are manufactured and assembled, the gap between the Roots rotors is measured using a feeler gauge. The feeler gauge is made up of multiple thin metal pieces of different thicknesses. The thickness of the metal piece that can be inserted into the gap between the Roots rotors corresponds to the gap between the Roots rotors.

[0006] However, the outer circumferential surface of each Roots rotor is composed of a combination of arcs and involute curves, and the junctions between the arcs and involute curves are not smooth. This prevents the metal piece of the feeler gauge from deforming along the outer circumferential surface of the Roots rotor, meaning only a metal piece with a thickness greater than the actual gap can be inserted into the gap between the Roots rotors. As a result, the feeler gauge may not be able to accurately measure the gap between the Roots rotors.

[0007] To provide a vacuum pump in which powder is less likely to be caught between root rotors, the root rotors can maintain smooth rotation, and the gap between the root rotors can be accurately measured using a feeler gauge. [Means for solving the problem]

[0008] 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, wherein each of the first Roots rotor and the second Roots rotor has an involute side surface having a shape formed by an involute curve, an arc-shaped convex surface located radially outward of the involute side surface, an arc-shaped concave surface located radially inward of the involute side surface, an outer smooth curved surface that smoothly connects the involute side surface and the arc-shaped convex surface, and an inner smooth curved surface that smoothly connects the involute side surface and the arc-shaped concave surface, wherein the radius of curvature of the arc-shaped convex surface is smaller than the radius of curvature of the arc-shaped concave surface.

[0009] In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface is shorter than the involute side surface. In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape consisting of a Bezier curve. In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a spline curve. In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape formed from a kernel curve. In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a natural spline curve. In one embodiment, each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a B-spline curve. In one embodiment, 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. [Effects of the Invention]

[0010] Because the radius of curvature of the convex arc surface of the first Roots rotor is smaller than that of the concave arc surface of the second Roots rotor, a minimum gap is formed between a point on the convex arc surface of the first Roots rotor and a point on the concave arc surface of the second Roots rotor. The gap between the Roots rotors gradually widens on both sides of this minimum gap. Therefore, powder is less likely to be trapped between the convex arc surface of the first Roots rotor and the concave arc surface of the second Roots rotor. As a result, the Roots rotors can maintain smooth rotation.

[0011] The involute side surface and the arc-shaped convex surface are smoothly connected by an outer smooth curved surface, and the involute side surface and the arc-shaped concave surface are smoothly connected by an inner smooth curved surface. Therefore, when measuring the gap between the first and second Roots rotors, the metal piece of the feeler gauge can deform smoothly along the outer surfaces of the first and second Roots rotors. As a result, the feeler gauge can accurately measure the gap between the first and second Roots rotors. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view illustrating an embodiment of a vacuum pump device. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 1 is an enlarged view of a Roots rotor. [Figure 4] FIG. 10 is an enlarged view showing an embodiment of an involute flank, an outer smooth curved surface, an inner smooth curved surface, an arc convex surface, and an arc concave surface. [Figure 5] FIG. 4 is an enlarged view illustrating the gap between the root rotors. [Figure 6] FIG. 1 shows two Roots rotors rotating in opposite directions. [Figure 7] FIG. 1 illustrates an embodiment of a three-lobed Roots rotor. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments 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 FIGS. 1 and 2 is a so-called dry vacuum pump device that does not use oil in the gas flow path. Because vaporized oil does not flow upstream, dry vacuum pump devices are suitable for use in semiconductor device manufacturing equipment that requires high cleanliness.

[0014] As shown in Figure 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 of 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 and 9 disposed in the rotor chamber 5, and a pair of rotary shafts 11 and 12 that support the Roots rotors 8 and 9. In one embodiment, the vacuum pump 1 may be a multi-stage vacuum pump having multiple Roots rotors disposed in multiple rotor chambers.

[0015] Although only the Roots rotor 8 and the rotating shaft 11 are shown in Figure 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. Figure 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.

[0016] The Roots rotors 8 and 9 do not contact each other, and do not contact 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.

[0017] 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.

[0018] 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 the 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 the process gas introduced into the process chamber.

[0019] The vacuum pump 1 further includes a gear housing 16 located outside the side wall 6A of the pump casing 6. A pair of meshing gears 20 are arranged inside the gear housing 16. Note that only one gear 20 is shown in FIG. 1. These gears 20 are fixed to 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.

[0020] 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 inside the motor housing 22.

[0021] In one embodiment, a pair of electric motors 2 may be provided, each coupled to a corresponding one of the rotating shafts 11 and 12. The pair of electric motors 2 are driven by a motor driver (not shown) to rotate in synchronous opposite directions, thereby rotating the rotating shafts 11 and 12 and the Roots rotors 8 and 9 in synchronous opposite directions, as shown in Fig. 2. In this case, the role of the gear 20 is to prevent the Roots rotors 8 and 9 from losing synchronization due to an unexpected external factor.

[0022] When the electric motor 2 rotates the Roots rotors 8, 9, gas is drawn into the rotor chamber 5 through the gas inlet 14. The rotation of the Roots rotors 8, 9 within the rotor chamber 5 sends the gas to the gas outlet 15, through which the gas is discharged from the pump casing 6.

[0023] The Roots rotors 8 and 9 have the same outer shape. Therefore, only the Roots rotor 8 will be described below. Figure 3 is an enlarged view of the Roots rotor 8. As shown in Figure 3, the Roots rotor 8 has an involute side surface 31 having a shape formed by an involute curve, an arc-shaped convex surface 34 located radially outward of the involute side surface 31, an outer smooth curved surface 35 that smoothly connects the involute side surface 31 and the arc-shaped convex surface 34, an arc-shaped concave surface 36 located radially inward of the involute side surface 31, and an inner smooth curved surface 37 that smoothly connects the involute side surface 31 and the arc-shaped concave surface 36.

[0024] 4 is an enlarged view showing one embodiment of the involute side surface 31, the outer smooth curved surface 35, the inner smooth curved surface 37, the arc convex surface 34, and the arc concave surface 36. As shown in FIG. 4, the outer smooth curved surface 35 is located between the arc convex surface 34 and the involute surface 31, and both ends of the outer smooth curved surface 35 are connected to the arc convex surface 34 and the involute surface 31, respectively. The inner smooth curved surface 37 is located between the involute surface 31 and the arc concave surface 36, and both ends of the inner smooth curved surface 37 are connected to the involute surface 31 and the arc concave surface 36, respectively. The outer smooth curved surface 35 and the inner smooth curved surface 37 are each shorter than the involute side surface 31.

[0025] As shown in FIG. 4, the outer smooth curved surface 35 smoothly connects the involute side surface 31 and the arc-shaped convex surface 34, and the inner smooth curved surface 37 smoothly connects the involute side surface 31 and the arc-shaped concave surface 36. Therefore, there are no corners on the outer circumferential surface of the Roots rotor 8. The Roots rotor 9 also has the same shape. Therefore, when measuring the gap between the Roots rotors 8 and 9, the metal piece of the feeler gauge can deform smoothly along the outer circumferential surfaces of the Roots rotors 8 and 9. As a result, the feeler gauge can accurately measure the gap between the Roots rotors 8 and 9.

[0026] In this embodiment, the outer smooth surface 35 and the inner smooth surface 37 each have a shape made up of a Bezier curve. A Bezier curve can make the outer smooth surface 35 and the inner smooth surface 37 smooth. In other embodiments, the outer smooth surface 35 and the inner smooth surface 37 each may have a shape made up of a spline curve, a kernel curve, a natural spline curve, or a B-spline curve. A kernel curve is a curve used to estimate the distribution of points using kernel density estimation. Factors that determine the shape of the kernel curve include the kernel function and the bandwidth. The kernel function is a function that determines the weight that influences each point, and the bandwidth is a parameter that determines the width of the kernel, which affects the smoothness of the kernel curve.

[0027] As shown in Figure 3, the Roots rotor 8 is a so-called two-lobe Roots rotor having two protrusions. Therefore, the Roots rotor 8 has two arc-shaped convex surfaces 34, four involute side surfaces 31, four outer smooth curved surfaces 35, four inner smooth curved surfaces 37, and two arc-shaped concave surfaces 36. The two arc-shaped convex surfaces 34 are connected to the outer ends of the four outer smooth curved surfaces 35, and the two arc-shaped concave surfaces 36 are connected to the inner ends of the four inner smooth curved surfaces 37. Each of the arc-shaped convex surfaces 34 and the arc-shaped concave surfaces 36 is longer than the involute side surfaces 31.

[0028] 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. 5 , 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 only one point on the arcuate concave surface 36 of the Roots rotor 9 are adjacent to each other, forming a minimum gap G1min between the arcuate convex surface 34 and the arcuate concave surface 36 of the Roots rotor 9. The width W of the space 40 formed between the arcuate convex surface 34 of the Roots rotor 8 and the arcuate concave surface 36 of the Roots rotor 9 gradually increases with increasing distance from the position where the minimum gap G1min is formed.

[0029] Because the radius of curvature R1 of the arc-shaped convex surface 34 of the Roots rotor 8 is smaller than the radius of curvature R2 of the arc-shaped concave surface 36 of the Roots rotor 9, a minimum gap G1min is formed between one point on the arc-shaped convex surface 34 of the Roots rotor 8 and one point on the arc-shaped concave surface 36 of the Roots rotor 9, and the gap between the Roots rotors 8 and 9 gradually widens on both sides of the minimum gap G1min. Therefore, powder is less likely to be pinched between the arc-shaped convex surface 34 of the Roots rotor 8 and the arc-shaped concave surface 36 of the Roots rotor 9. As a result, the Roots rotors 8 and 9 can maintain smooth rotation.

[0030] FIG. 6 shows two Roots rotors 8 and 9 rotating in opposite directions. As shown in FIG. 6, the involute side surfaces 31 of the Roots rotors 8 and 9 face each other, but do not face the arc-shaped convex surface 34 or the arc-shaped concave surface 36. Meanwhile, the arc-shaped convex surface 34 of the Roots rotor 8 faces the arc-shaped concave surface 36 of the Roots rotor 9, but does not face the involute side surface 31 of the Roots rotor 9. Similarly, the arc-shaped convex surface 34 of the Roots rotor 9 faces the arc-shaped concave surface 36 of the Roots rotor 8, but does not face the involute side surface 31 of the Roots rotor 8. During one rotation of the Roots rotors 8 and 9, the Roots rotors 8 and 9 do not make line contact but make point contact (actually, no contact). Therefore, powder is less likely to be trapped between the Roots rotors 8 and 9. The gap G2 between the involute side surfaces 31 of the two Roots rotors 8 and 9 is always constant.

[0031] 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 this point contact (actually non-contact) of the involute side surfaces 31, powder is unlikely to become trapped between the involute side surfaces 31 of the Roots rotor 8 and the involute side surfaces 31 of the Roots rotor 9.

[0032] The Roots rotors 8 and 9 in the above-described embodiments are two-lobed Roots rotors with two lobes. However, the present invention is not limited to the above-described embodiments and can also be applied to a three-lobed Roots rotor with three lobes or a multi-lobe Roots rotor with four or more lobes.

[0033] For example, Figure 7 shows an embodiment of a three-lobe Root rotor. In this embodiment, each of the Root rotors 51 and 52 includes an involute side surface 31 having a shape formed by an involute curve, an arc-shaped convex surface 34 located radially outward of the involute side surface 31, an outer smooth curved surface 35 smoothly connecting the involute side surface 31 and the arc-shaped convex surface 34, an arc-shaped concave surface 36 located radially inward of the involute side surface 31, and an inner smooth curved surface 37 smoothly connecting the involute side surface 31 and the arc-shaped concave surface 36. The radius of curvature R3 of the arc-shaped convex surface 34 is smaller than the radius of curvature R4 of the arc-shaped concave surface 36. The configurations of the three-lobe Root rotors 51 and 52 in this embodiment, which are not specifically described, are the same as those of the above-described embodiment described with reference to Figures 1 to 6, and therefore, redundant description will be omitted.

[0034] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may 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 in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0035] 1. Vacuum pump 2 electric motor 2A motor rotor 2B Motor Stator 5. Rotor chamber 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 gears 22 Motor housing 31 Involute side 34 Convex arc 35 Outer smooth surface 36 Concave arc 37 Inner smooth surface 40 space

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-shaped convex surface located radially outward of the involute side surface, an arc-shaped concave surface located radially inward of the involute side surface, an outer smooth curved surface that smoothly connects the involute side surface and the arc-shaped convex surface, and an inner smooth curved surface that smoothly connects the involute side surface and the arc-shaped concave 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 outer smooth curved surface and the inner smooth curved surface is shorter than the involute side surface.

3. 2. The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape consisting of a Bezier curve.

4. 2. The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a spline curve.

5. The vacuum pump of claim 1 , wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape consisting of a kernel curve.

6. 2. The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a natural spline curve.

7. 2. The vacuum pump according to claim 1, wherein each of the outer smooth curved surface and the inner smooth curved surface has a shape formed by a B-spline curve.

8. 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.

9. 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.

10. 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.

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