Vacuum pump

Abstract

Provided is a vacuum pump in which powder is unlikely to be sandwiched between roots rotors, smooth rotation of the roots rotors can be maintained, and a gap between the roots rotors can be accurately measured using a gap gauge. The first roots rotor (8) and the second roots rotor (9) each have: an involute side surface (31) having a shape comprising an involute curve; an arcuate convex surface (34) positioned on the radially outer side of the involute side surface (31); an arcuate concave surface (36) positioned on the radially inner side of the involute side surface (31); an outer smooth curved surface (35) that smoothly connects the involute side surface (31) and the arcuate convex surface (34); and an inner smooth curved surface (37) that smoothly connects the involute side surface (31) and the arcuate concave surface (36). 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).

Description

TECHNICAL FIELD

[0001] The present application relates to a vacuum pump, and particularly to a vacuum pump suitable for exhausting process gas used in the manufacture of semiconductor devices, liquid crystal panels, LEDs, solar cells, and the like. BACKGROUND

[0002] In the manufacturing process of semiconductor devices, liquid crystal panels, LEDs, solar cells, and the like, process gas is introduced into a process chamber to perform various processes such as etching, CVD, and the like. The process gas introduced into the process chamber is exhausted by a vacuum pump. Generally, the vacuum pump used in these manufacturing processes requiring high cleanliness is a so-called dry vacuum pump that does not use oil in the gas flow path. As a representative example of such a dry vacuum pump, there is a positive displacement vacuum pump that transports gas by causing a pair of Roots rotors disposed in a rotor chamber to rotate in opposite directions.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. H1-077782

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] Process gas sometimes contains powder composed of by-products. Such powder flows into the vacuum pump along with the process gas. In addition, depending on the state (e.g., temperature, pressure) in the vacuum pump, powder can also be generated in the vacuum pump after the process gas flows into the vacuum pump. Most of the powder is exhausted from the vacuum pump along with the process gas, but a part of the powder remains in the rotor chamber and gradually accumulates in the rotor chamber. In particular, when the convex and concave surfaces of the two opposing Roots rotors are in a state of surface contact (actually non-contact), the powder is strongly pinched by the convex and concave surfaces of the Roots rotors since there is no place for the powder to escape, and sometimes hinders the rotation of the Roots rotors.

[0008] On the other hand, in order to improve the pump efficiency, it is desirable that the gap between the Roots rotors be as small as possible. Therefore, after the Roots rotors are manufactured and assembled, a gap gauge is used to measure the gap between the Roots rotors. The gap gauge is composed of a plurality of thin metal pieces having 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.

[0009] However, the outer peripheral surface of each Roots rotor is composed of a combination of a circular arc and an involute curve, and the connection portion of the circular arc and the involute curve is not smoothly connected. Therefore, the metal piece of the gap gauge cannot be deformed along the outer peripheral surface of the Roots rotor, and only a metal piece having a thickness smaller than the actual gap can be inserted into the gap between the Roots rotors. As a result, the gap gauge sometimes cannot correctly measure the gap between the Roots rotors. SUMMARY

[0010] The present application provides a vacuum pump in which powder is less likely to be caught between the roots, smooth rotation of the roots is maintained, and the gap between the roots can be accurately measured using a gap gauge.

[0011] Technical means for solving the technical problem

[0012] In one embodiment, a vacuum pump is provided, including: a pump housing having at least one rotor chamber inside; and first and second roots arranged side by side in the rotor chamber, the first and second roots each having: an involute side having a shape composed of an involute curve; a circular-arc convex surface located radially outward of the involute side; a circular-arc concave surface located radially inward of the involute side; an outer smooth surface smoothly connecting the involute side and the circular-arc convex surface; and an inner smooth surface smoothly connecting the involute side and the circular-arc concave surface, the circular-arc convex surface having a smaller radius of curvature than the circular-arc concave surface.

[0013] In one embodiment, the outer and inner smooth surfaces are each shorter than the involute side.

[0014] In one embodiment, the outer and inner smooth surfaces each have a shape composed of a Bezier curve.

[0015] In one embodiment, the outer and inner smooth surfaces each have a shape composed of a spline curve.

[0016] In one embodiment, the outer and inner smooth surfaces each have a shape composed of a kernel curve.

[0017] In one embodiment, the outer and inner smooth surfaces each have a shape composed of a natural spline curve.

[0018] In one embodiment, the outer and inner smooth surfaces each have a shape composed of a B-spline curve.

[0019] In one embodiment, the circular-arc convex surface and the circular-arc concave surface are each longer than the involute side.

[0020] In one embodiment, the width of the space between the circular-arc convex surface and the circular-arc concave surface increases as it moves away from the position of the smallest gap between the circular-arc convex surface and the circular-arc concave surface.

[0021] In one mode, the radius of curvature of the convex circular arc is 0.2 to 0.9 times the radius of curvature of the concave circular arc.

[0022] Effects of the Invention

[0023] Since the radius of curvature of the convex circular arc of the first Roots rotor is smaller than the radius of curvature of the concave circular arc of the second Roots rotor, a point on the convex circular arc of the first Roots rotor and a point on the concave circular arc of the second Roots rotor form a minimum gap, and on both sides of the minimum gap, the gap between the Roots rotors gradually increases. Therefore, it is difficult for powder to be caught between the convex circular arc of the first Roots rotor and the concave circular arc of the second Roots rotor. As a result, the Roots rotors can maintain smooth rotation.

[0024] The involute side surface is smoothly connected to the convex circular arc by an outer smooth curved surface, and the involute side surface is smoothly connected to the concave circular arc by an inner smooth curved surface. Therefore, when measuring the gap between the first Roots rotor and the second Roots rotor, the metal sheet of the gap gauge can be smoothly deformed along the outer peripheral surfaces of the first Roots rotor and the second Roots rotor. As a result, the gap gauge can accurately measure the gap between the first Roots rotor and the second Roots rotor. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a sectional view showing one embodiment of a vacuum pump device.

[0026] Figure 2 is Figure 1 is a sectional view taken along line A-A of

[0027] Figure 3 is an enlarged view of a Roots rotor.

[0028] Figure 4 is an enlarged view showing one embodiment of an involute side surface, an outer smooth curved surface, an inner smooth curved surface, a convex circular arc, and a concave circular arc.

[0029] Figure 5 is an enlarged view illustrating a gap between Roots rotors.

[0030] Figure 6 is a view showing a state in which two Roots rotors are rotating in opposite directions.

[0031] Figure 7 is a view showing one embodiment of a three-bladed Roots rotor.

[0032] SYMBOL EXPLANATION

[0033] 1 vacuum pump

[0034] 2 motor

[0035] 2A motor rotor

[0036] 2B motor stator

[0037] 5 rotor chamber

[0038] 6 pump housing

[0039] 8, 9 Roots rotor

[0040] 11, 12 rotating shaft

[0041] 14 gas inlet

[0042] 15 gas outlet

[0043] 16 gear box

[0044] 17 bearing

[0045] 18 bearing

[0046] 20 gear

[0047] 22 motor housing

[0048] 31 involute side surface

[0049] 34 circular-arc convex surface

[0050] 35 outer smooth curved surface

[0051] 36 circular-arc concave surface

[0052] 37 inner smooth curved surface

[0053] 40 space DETAILED DESCRIPTION

[0054] Hereinafter, an embodiment of the present application will be described with reference to the accompanying drawings. Figure 1 is a sectional view showing one embodiment of a vacuum pump apparatus, Figure 2 is Figure 1 A-A line sectional view of FIG. 1. The vacuum pump apparatus of the embodiment described hereinafter is a positive displacement type vacuum pump apparatus. In particular, Figure 1 and Figure 2 the vacuum pump apparatus shown in FIGS. 1 and 2 is a so-called dry type vacuum pump apparatus which does not use oil in a gas flow path. Since the dry type vacuum pump apparatus does not cause vaporized oil to flow to an upstream side, it is suitable for use in a manufacturing apparatus of a semiconductor device which requires high cleanliness.

[0055] As Figure 1As shown, the vacuum pump device is provided with a vacuum pump 1 and a motor 2 that drives the vacuum pump 1. The vacuum pump 1 of the present embodiment is a single-stage vacuum pump. That is, the vacuum pump 1 is provided with a pump casing 6 that has a rotor chamber 5 inside, single-stage Roots rotors 8, 9 disposed inside the rotor chamber 5, and a pair of rotary shafts 11, 12 that support the Roots rotors 8, 9. In one embodiment, the vacuum pump 1 can also be a multi-stage vacuum pump having multi-stage Roots rotors disposed inside a plurality of rotor chambers.

[0056] In Figure 1 , only the Roots rotor 8 and the rotary shaft 11 are shown, but the Roots rotor 8 and the Roots rotor 9 are disposed side by side inside the pump casing 6, and the rotary shaft 11 and the rotary shaft 12 are disposed side by side. Figure 2 The Roots rotor 8 and the Roots rotor 9 are shown disposed side by side. The Roots rotor 8 is supported by the rotary shaft 11, and the Roots rotor 9 is supported by the rotary shaft 12.

[0057] The Roots rotor 8 and the Roots rotor 9 are in non-contact with each other, and the Roots rotors 8, 9 are in non-contact with the inner surface of the pump casing 6. Therefore, the Roots rotors 8, 9 can rotate smoothly inside the pump casing 6 without using lubricating oil.

[0058] The Roots rotor 8 and the rotary shaft 11 can be an integrated structure. Similarly, the Roots rotor 9 and the rotary shaft 12 can be an integrated structure. The motor 2 is linked to one of the rotary shafts 11, 12. In one embodiment, it can also be that a pair of motors 2 are linked to the rotary shafts 11, 12, respectively.

[0059] 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 linked to a chamber (not shown) that is filled with a gas to be transported. In one example, the gas inlet 14 is linked to a process chamber of a manufacturing device for semiconductor devices, and the vacuum pump 1 is used to exhaust a process gas that is introduced into the process chamber.

[0060] The vacuum pump 1 is also provided with a gear box 16 that is located outside a side wall 6A of the pump casing 6. Inside the gear box 16, a pair of gears 20 that mesh with each other are disposed. Further, in Figure 1 , only one gear 20 is depicted. The gears 20 are fixed to the rotary shafts 11, 12, respectively. The motor 2 is rotated by a motor driver (not shown), and one of the rotary shafts 11, 12 that is linked to the motor 2 causes the other of the rotary shafts 11, 12 that is not linked to the motor 2 to be counter-rotated via the gears 20.

[0061] The rotary shafts 11, 12 are rotatably supported by a bearing 17 held to the side wall 6A of the pump case 6 and a bearing 18 held to the other side wall 6B of the pump case 6. The electric motor 2 has a motor case 22 located outside the side wall 6B of the pump case 6 and a motor rotor 2A and a motor stator 2B disposed in the motor case 22.

[0062] In one embodiment, a pair of electric motors 2 can also be provided, which are respectively connected to the rotary shafts 11, 12. The pair of electric motors 2 are synchronously and reversely rotated by a motor driver not shown, as Figure 2 indicated, to synchronously and reversely rotate the rotary shafts 11, 12 and the Roots rotors 8, 9. The gear 20 in this case functions to prevent the synchronous rotation of the Roots rotors 8, 9 from falling out of step due to a sudden external factor.

[0063] 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 gas is sent to the gas outlet 15 by the rotation of the Roots rotors 8, 9 in the rotor chamber 5 and is discharged from the pump case 6 through the gas outlet 15.

[0064] The Roots rotors 8, 9 have the same outer shape. Therefore, the following describes the Roots rotor 8. Figure 3 is an enlarged view of the Roots rotor 8. As Figure 3 indicated, the Roots rotor 8 has an involute side surface 31 having a shape composed of an involute curve, a circular-arc convex surface 34 located radially outside the involute side surface 31, an outer smooth curved surface 35 smoothly connecting the involute side surface 31 and the circular-arc convex surface 34, a circular-arc concave surface 36 located radially inside the involute side surface 31, and an inner smooth curved surface 37 smoothly connecting the involute side surface 31 and the circular-arc concave surface 36.

[0065] Figure 4 is an enlarged view of one embodiment of the involute side surface 31, the outer smooth curved surface 35, the inner smooth curved surface 37, the circular-arc convex surface 34, and the circular-arc concave surface 36. As Figure 4 indicated, the outer smooth curved surface 35 is located between the circular-arc convex surface 34 and the involute side surface 31, and both ends of the outer smooth curved surface 35 are connected to the circular-arc convex surface 34 and the involute side surface 31, respectively. The inner smooth curved surface 37 is located between the involute side surface 31 and the circular-arc concave surface 36, and both ends of the inner smooth curved surface 37 are connected to the involute side surface 31 and the circular-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.

[0066] As Figure 4As shown, since the outer smooth curved surface 35 smoothly connects the involute side surface 31 to the arcuate convex surface 34, and the inner smooth curved surface 37 smoothly connects the involute side surface 31 to the arcuate concave surface 36, 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 rotor 8 and the Roots rotor 9, the metal strip of the gap gauge can smoothly deform along the outer circumferential surfaces of the Roots rotor 8 and the Roots rotor 9. As a result, the gap gauge can accurately measure the gap between the Roots rotor 8 and the Roots rotor 9.

[0067] In this embodiment, the outer smooth surface 35 and the inner smooth surface 37 each have a shape formed by a Bézier curve. The Bézier curve enables the outer smooth surface 35 and the inner smooth surface 37 to become smooth surfaces. In other embodiments, the outer smooth surface 35 and the inner smooth surface 37 may also each have a shape formed by a spline curve, a kernel curve, a natural spline curve, or a B-spline curve. A kernel curve is a curve that uses kernel density estimation to estimate the point distribution. Factors determining the shape of the kernel curve include the kernel function and bandwidth. The kernel function is a function that determines the weight of the influence on each point, and the bandwidth is a parameter that determines the width of the kernel and affects the smoothness of the kernel curve.

[0068] like Figure 3 As shown, the Roots rotor 8 is a so-called two-lobe Roots rotor with two protrusions. Therefore, the Roots rotor 8 has two arcuate convex surfaces 34, four involute side surfaces 31, four outer smooth curved surfaces 35, four inner smooth curved surfaces 37, and two arcuate concave surfaces 36. The two arcuate convex surfaces 34 are connected to the outer ends of the four outer smooth curved surfaces 35, and the two arcuate concave surfaces 36 are connected to the inner ends of the four inner smooth curved surfaces 37. Each of the arcuate convex surfaces 34 and arcuate concave surfaces 36 is longer than the involute side surfaces 31.

[0069] The radius of curvature R1 of the convex arc surface 34 is smaller than the radius of curvature R2 of the concave arc surface 36. In one embodiment, the radius of curvature R1 of the convex arc surface 34 is 0.2 to 0.9 times the radius of curvature R2 of the concave arc surface 36. Therefore, as... Figure 5 As shown, when the convex arc surface 34 of the Roots rotor 8 and the concave arc surface 36 of the Roots rotor 9 are opposite each other, only a point on the convex arc surface 34 of the Roots rotor 8 is close to a point on the concave arc surface 36 of the Roots rotor 9, forming a minimum gap G1min between the convex arc surface 34 and the concave arc surface 36. The width W of the space 40 formed between the convex arc surface 34 of the Roots rotor 8 and the concave arc surface 36 of the Roots rotor 9 gradually increases as the distance from the position where the minimum gap G1min is formed increases.

[0070] Since the radius of curvature Rl of the circular-arc convex surface 34 of the Roots rotor 8 is smaller than the radius of curvature R2 of the circular-arc concave surface 36 of the Roots rotor 9, a point on the circular-arc convex surface 34 of the Roots rotor 8 and a point on the circular-arc concave surface 36 of the Roots rotor 9 form a minimum gap Glmin, and on both sides of the minimum gap Glmin, the gap between the Roots rotors 8, 9 gradually increases. Therefore, it is difficult for powder to be caught between the circular-arc convex surface 34 of the Roots rotor 8 and the circular-arc concave surface 36 of the Roots rotor 9. As a result, the Roots rotors 8, 9 can maintain smooth rotation.

[0071] Figure 6 is a view showing a state in which the two Roots rotors 8, 9 are rotating in opposite directions. As shown in Figure 6 the involute side surface 31 of the Roots rotor 8 and the involute side surface 31 of the Roots rotor 9 face each other, and the circular-arc convex surface 34 and the circular-arc concave surface 36 do not face each other. On the other hand, the circular-arc convex surface 34 of the Roots rotor 8 faces the circular-arc concave surface 36 of the Roots rotor 9, and does not face the involute side surface 31 of the Roots rotor 9. Similarly, the circular-arc convex surface 34 of the Roots rotor 9 faces the circular-arc concave surface 36 of the Roots rotor 8, and does not face the involute side surface 31 of the Roots rotor 8. During one rotation of the Roots rotor 8 and the Roots rotor 9, the Roots rotor 8 and the Roots rotor 9 do not linearly contact each other, but point contact (actually, non-contact). Therefore, it is difficult for powder to be caught between the Roots rotor 8 and the Roots rotor 9. The gap G2 between the involute side surfaces 31 of the two Roots rotors 8, 9 is always constant.

[0072] The involute side surface 31 is a surface curved outward. Therefore, a gap G2 is formed between a point on the involute side surface 31 of the Roots rotor 8 and a point on the involute side surface 31 of the Roots rotor 9, and on both sides of the gap G2, the gap increases. Through such point contact (actually, non-contact) of the involute side surfaces 31, it is difficult for powder to be caught between the involute side surface 31 of the Roots rotor 8 and the involute side surface 31 of the Roots rotor 9.

[0073] The Roots rotors 8, 9 of the above-described embodiment are two-blade Roots rotors having two protruding portions, but the present application is not limited to the above-described embodiment, and can be applied to three-blade Roots rotors having three protruding portions or multi-blade Roots rotors having four or more protruding portions.

[0074] For example, Figure 7This diagram illustrates one embodiment of a three-lobe Roots rotor. In this embodiment, each of the Roots rotors 51 and 52 also includes: an involute side surface 31 having a shape formed by an involute curve; a circular arc convex surface 34 located radially outward of the involute side surface 31; an outer smooth surface 35 smoothly connecting the involute side surface 31 and the circular arc convex surface 34; a circular arc concave surface 36 located radially inward of the involute side surface 31; and an inner smooth surface 37 smoothly connecting the involute side surface 31 and the circular arc concave surface 36. The radius of curvature R3 of the circular arc convex surface 34 is smaller than the radius of curvature R4 of the circular arc concave surface 36. The structure of the three-lobe Roots rotors 51 and 52, unless otherwise specified in this embodiment, is referenced. Figures 1 to 6 The above-described implementation methods are the same, so repeated descriptions are omitted.

[0075] The above embodiments are described to enable those skilled in the art to implement the present invention. Those skilled in the art will naturally be able to implement various modifications of the above embodiments, and the technical concept of the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but should be interpreted as encompassing the broadest scope of the technical concept as defined by the scope of the patent claims.

Claims

1. A vacuum pump, characterized by, Possessing: a pump housing having at least one rotor chamber inside; and a first Roots rotor and a second Roots rotor arranged side by side in the rotor chamber, the first and second Roots rotors each having: an involute side having a shape composed of an involute curve; a circular-arc convex surface located on a radially outer side of the involute side; a circular-arc concave surface located on a radially inner side of the involute side; an outer-side smooth curve smoothly connecting the involute side and the circular-arc convex surface; and an inner-side smooth curve smoothly connecting the involute side and the circular-arc concave surface, the circular-arc convex surface having a smaller radius of curvature than the circular-arc concave surface.

2. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve are each shorter than the involute side.

3. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve each have a shape composed of a Bezier curve.

4. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve each have a shape composed of a spline curve.

5. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve each have a shape composed of a kernel curve.

6. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve each have a shape composed of a natural spline curve.

7. The vacuum pump according to claim 1, wherein the outer-side smooth curve and the inner-side smooth curve each have a shape composed of a B-spline curve.

8. The vacuum pump according to claim 1, wherein the circular-arc convex surface and the circular-arc concave surface are each longer than the involute side.

9. The vacuum pump according to claim 1, wherein a width of a space formed between the circular-arc convex surface and the circular-arc concave surface when the circular-arc convex surface and the circular-arc concave surface are opposed increases as it moves away from a position of a minimum gap between the circular-arc convex surface and the circular-arc concave surface.

10. The vacuum pump according to claim 1, wherein the radius of curvature of the circular-arc convex surface is 0.2 to 0.9 times the radius of curvature of the circular-arc concave surface.

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