Vacuum pump

Abstract

To provide a vacuum pump that can reduce mechanical loss, and is low in cost.SOLUTION: A vacuum pump comprises: a casing comprising a suction port and a discharge port; a rotor arranged in the casing, and attached to a rotating shaft of a motor; a first bearing arranged between the motor and the rotor, and rotatably supporting the rotating shaft; and a second bearing arranged on the side opposite to the motor with respect to the rotor, and rotatably supporting the rotating shaft. The first bearing is a permanent magnet type magnetic bearing.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a vacuum pump.

Background Art

[0002] Conventionally, a vacuum pump has been used, for example, to exhaust a process gas in a vacuum chamber where a semiconductor manufacturing apparatus is disposed. Generally, in a semiconductor manufacturing process, it is required that the inside of the vacuum chamber be a clean atmosphere. Therefore, as the vacuum pump, a dry vacuum pump that does not use oil in the gas flow path inside the pump is used. As such a dry vacuum pump, for example, a two-axis Roots type positive displacement dry vacuum pump is known.

[0003] A two-axis Roots type positive displacement dry vacuum pump includes a pair of opposed Roots type rotors in a casing, and a clearance is provided so that the gaps between these rotors and between the rotors and the casing become minute. Then, by the synchronous reverse rotation of this pair of rotors, the process gas that has entered from the intake port is confined in the space formed between the rotor and the casing and transferred to the exhaust port side.

[0004] Patent Document 1 proposes a dry vacuum pump that employs a ceramic ball bearing as a bearing for supporting the rotation shaft of a rotor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when a rotating body that rotates at high speed is supported by a ball bearing, the diameter of the bearing becomes large, so the mechanical loss becomes large and the rotation speed is limited.

[0007] The present invention has been made in consideration of the above points. An object of the present invention is to provide a vacuum pump that can reduce mechanical losses and is low in cost.

Means for Solving the Problems

[0008] The vacuum pump according to the first aspect of the present invention includes a casing having a suction port and a discharge port, a rotor disposed in the casing and attached to the rotating shaft of the motor, a first bearing disposed between the motor and the rotor and rotatably supporting the rotating shaft, a second bearing disposed on the side opposite to the motor with respect to the rotor and rotatably supporting the rotating shaft, and the first bearing is a permanent magnetic bearing (PMB).

[0009] According to such an aspect, since the first bearing is a permanent magnetic bearing, mechanical losses can be reduced compared to the case of a mechanical bearing, and the rotor can be rotated at a high speed. Also, compared to the case of a controlled magnetic bearing, bearing control is not required, and the cost is low.

[0010] The vacuum pump according to the second aspect of the present invention is the vacuum pump according to the first aspect, wherein the motor is a radial gap type motor.

[0011] The vacuum pump according to the third aspect of the present invention is the vacuum pump according to the first aspect, wherein the motor is an axial gap type motor.

[0012] The vacuum pump according to the fourth aspect of the present invention is the vacuum pump according to any one of the first to third aspects, The first bearing has an inner magnet fixed to the rotating shaft and an outer magnet disposed radially outside the inner magnet and fixed to the casing. The inner magnet is displaced toward the second bearing side with respect to the outer magnet, and the rotating shaft is biased toward the second bearing side by the axial repulsive force between the inner magnet and the outer magnet.

[0013] According to such an aspect, when the motor is an axial gap type motor, the rotating shaft is pulled toward the motor side by the axial magnetic force generated by the motor. However, the axial repulsive force between the inner magnet and the outer magnet of the first bearing biases the rotating shaft toward the second bearing side, thereby being able to counteract the pulling force from the motor. As a result, the movement of the rotating shaft in the axial direction can be suppressed, and the rotation can be stabilized. Further, when using a vacuum pump with the rotor disposed above the motor, the rotating shaft receives downward (i.e., toward the motor side) gravity, but the axial repulsive force between the inner magnet and the outer magnet of the first bearing biases the rotating shaft toward the second bearing side (i.e., upward), thereby being able to support the weight of the rotating shaft. As a result, the movement of the rotating shaft in the axial direction can be suppressed, and the rotation can be stabilized.

[0014] The vacuum pump according to the fifth aspect of the present invention is the vacuum pump according to the second aspect, further comprising a third bearing disposed on the side opposite to the rotor with respect to the motor and rotatably supporting the rotating shaft.

[0015] According to such an aspect, the rotating shaft is pulled in the radial direction by the radial magnetic force generated by the radial gap type motor. However, since the end portion of the rotating shaft on the motor side can be supported by the third bearing, the movement of the rotating shaft in the radial direction (tilting with the second bearing as a fulcrum) can be suppressed, and the rotation can be stabilized.

[0016] The vacuum pump according to the sixth aspect of the present invention is the vacuum pump according to any one of the first to fifth aspects, The inner magnet and the outer magnet each have a plurality of unit magnets laminated in the axial direction.

[0017] According to such an aspect, it is possible to arbitrarily combine the magnetization directions of the plurality of unit magnets laminated in the axial direction, and thereby adjust the axial rigidity and the radial rigidity of the first bearing. For example, by laminating unit magnets having the same magnetization direction in the axial direction, the repulsive force between the inner magnet and the outer magnet can be increased, and thereby the axial rigidity and the radial rigidity of the first bearing can be adjusted. Further, for example, by laminating unit magnets having a magnetization direction in the axial direction and unit magnets in the radial direction alternately and in a rotating direction (i.e., in a Halbach array), the repulsive force between the inner magnet and the outer magnet can be increased, and thereby the axial rigidity and the radial rigidity of the first bearing can be adjusted.

[0018] The vacuum pump according to the seventh aspect of the present invention is the vacuum pump according to any one of the first to sixth aspects, wherein the second bearing is a permanent magnet type magnetic bearing.

[0019] According to such an aspect, compared with the case where the second bearing is a mechanical bearing, mechanical loss can be further reduced, and the rotor can be rotated at a higher speed.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a vacuum pump that can reduce mechanical loss and is low in cost.

Brief Description of the Drawings

[0021]

Figure 1

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Figure 10

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Figure 13

Mode for Carrying Out the Invention

[0022] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In the following description and the drawings used in the following description, the same reference numerals are used for parts that can be configured identically, and redundant descriptions are omitted.

[0023] (First Embodiment) FIG. 1 is a front view showing a schematic configuration of a vacuum pump 10 according to a first embodiment, and FIG. 2 is a side view thereof. FIG. 3 is a view showing a cross section of the vacuum pump 10 shown in FIG. 1 taken along line A-A. FIG. 4 is a view showing a cross section of the vacuum pump shown in FIG. 2 taken along line B-B. FIG. 5 is a view showing a cross section of the vacuum pump shown in FIG. 4 taken along line C-C. The vacuum pump 10 according to the present embodiment is installed in, for example, a semiconductor manufacturing apparatus and is used to evacuate a process gas in a vacuum chamber.

[0024] As shown in FIGS. 1 to 5, the vacuum pump 10 includes a casing 11 having a suction port 13 and a discharge port 14, a motor 12, and rotors 15a and 15b disposed in the casing 11 and attached to the rotating shafts 16a and 16b of the motor 12.

[0025] In the illustrated example, the motor 12 includes a pair of rotating shafts 16a and 16b extending parallel to each other, a rotor 23 including permanent magnets fixed to each of the pair of rotating shafts 16a and 16b, a stator 24 including electromagnets disposed to face the rotor 23, and a housing 20 that supports the stator 24.

[0026] In the present embodiment, the motor 12 is a radial gap type motor, and the stator 24 is disposed on the outer side in the radial direction of the rotor 23 when viewed from the central axis of each of the rotating shafts 16a and 16b. In the illustrated example, each rotor 23 has six poles, and the stator 24 has a total of twelve slots. By controlling the current flowing through each electromagnet of the stator 24, the pair of rotating shafts 16a and 16b are rotated (reversed) in opposite directions to each other together with the rotors 15a and 15b by the magnetic force generated between the rotor 23 and the stator 24.

[0027] In the illustrated example, the rotors 15a and 15b are roots-type rotors. However, the rotors 15a and 15b in the present invention are not limited to the roots type, and may be, for example, scroll type, rotary vane type, claw type, screw type, etc. Clearances are provided so that the gaps between the pair of rotors 15a and 15b and between the rotors 15a and 15b and the casing 11 become minute. Referring to FIG. 3, when the pair of rotors 15a and 15b are synchronously reversed by the rotational power from the motor 12, the process gas that has entered from the suction port 13 is confined in the space formed between the rotors 15a and 15b and the casing 11 and is transferred to the discharge port 14 side.

[0028] The exhaust speed of the vacuum pump 10 is not particularly limited, and may be 100,000 L / min or less, or may be 50,000 L / min or less, or may be 10,000 L / min or less. As an example, the output of the motor 12 is 125 W on two axes, the axial length (vertical length in FIG. 1) of the vacuum pump 10 is 220 mm, the width (horizontal length in FIG. 1) is 180 mm, the axial length of the rotors 15a and 15b is 120 mm, the outer diameter is φ76 mm, the distance between the central axes of each of the pair of rotors 15a and 15b is 56 mm, the rotational speed is 30,000 / min, and the exhaust speed may be 8,300 L / min.

[0029] As shown in FIG. 4, the vacuum pump 10 has first bearings 17a and 17b and second bearings 18a and 18b that rotatably support a pair of rotating shafts 16a and 16b, respectively.

[0030] The first bearings 17a and 17b are arranged between the motor 12 and the rotors 15a and 15b, and the second bearings 18a and 18b are arranged on the side opposite to the motor 12 with respect to the rotors 15a and 15b. As shown in FIG. 4, first seal portions 31a and 31b formed of screw grooves are provided between the first bearings 17a and 17b and the rotors 15a and 15b, and the atmosphere inside the casing 11 is sealed with respect to the first bearings 17a and 17b side. Also, second seal portions 32a and 32b formed of screw grooves are provided between the second bearings 18a and 18b and the rotors 15a and 15b, and the atmosphere inside the casing 11 is sealed with respect to the second bearings 18a and 17b side.

[0031] In the illustrated example, the second bearings 18a and 18b are ball bearings. As an example, the inner diameter of the ball bearing may be φ4 mm, the outer diameter may be φ8 mm, the axial thickness Lg may be 2 mm, the allowable rotational speed may be 61,000 rpm, and the mechanical loss may be 20 W.

[0032] In the present embodiment, the first bearings 17a and 17b are permanent magnetic bearings (PMB). The definition of the term "permanent magnetic bearing" is based on the provisions of JIS B0913-1:2013.

[0033] FIG. 6 is a perspective view showing an example of the configuration of the first bearings 17a and 17b (permanent magnetic bearings). As shown in FIGS. 4 and 6, the first bearings 17a and 17b include an inner magnet 21 made of an annular permanent magnet fixed to the rotating shafts 16a and 16b, and an outer magnet 22 made of an annular permanent magnet arranged radially outside the inner magnet 21 and fixed to the casing 11. In the example shown in FIG. 4, both the inner magnet 21 and the outer magnet 22 are magnetized parallel to the axial direction, but the present invention is not limited thereto, and both the inner magnet 21 and the outer magnet 22 may be magnetized in the radial direction (radial direction).

[0034] As shown in FIGS. 4 and 6, the inner magnet 21 is displaced and arranged toward the second bearings 18a and 18b side (upward in FIG. 4) with respect to the outer magnet 22, and the axial repulsive force between the inner magnet 21 and the outer magnet 22 biases the rotary shafts 16a and 16b toward the second bearings 18a and 18b side (upward in FIG. 4).

[0035] In the examples shown in FIGS. 4 and 6, the inner magnet 21 and the outer magnet 22 are each composed of a single layer of magnets. However, the present embodiment is not limited to this. For example, as shown in FIGS. 11 and 12, the inner magnet 21 and the outer magnet 22 may each be composed of a plurality of (five layers in the illustrated example) unit magnets 121 and 122 laminated in the axial direction. In this case, the number of layers and the magnetization direction of the unit magnets 121 and 122 laminated in the axial direction can be arbitrarily combined, whereby the axial rigidity and the radial rigidity of the first bearings 17a and 17b can be adjusted.

[0036] FIG. 11 is a longitudinal sectional view showing a modified example of the configuration of the first bearings 17a and 17b (permanent magnet type magnetic bearings). In the example shown in FIG. 11, the magnetization direction of each unit magnet 121 of the inner magnet 21 is the same direction in the axial direction (upward in FIG. 11), and the magnetization direction of each unit magnet 122 of the outer magnet 22 is also the same direction in the axial direction and the same direction as that of the unit magnet 121 of the inner magnet 21 (upward in FIG. 11). As shown in FIG. 11, by laminating a plurality of unit magnets 121 and 122 having the same magnetization direction in the axial direction (upward in the illustrated example), the repulsive force between the inner magnet 21 and the outer magnet 22 can be increased. Therefore, by adjusting the number of layers of the unit magnets 121 and 122, it is possible to adjust the axial rigidity and the radial rigidity of the first bearings 17a and 17b.

[0037] FIG. 12 is a longitudinal sectional view showing another modified example of the configuration of the first bearings 17a and 17b (permanent magnet type magnetic bearings). In the example shown in FIG. 12, in the inner magnet 21, the magnetization direction is the axial direction for the unit magnets 121 (the unit magnets 121 in the 2nd and 4th layers in FIG. 12), and the magnetization direction is the radial direction (radial direction) for the unit magnets 121 (the unit magnets 121 in the 1st, 3rd, and 5th layers in FIG. 12), and they are laminated alternately and in a direction-rotating manner (i.e., in a Halbach array). In the outer magnet 22, the magnetization direction is the axial direction and the unit magnets 121 have the same direction as the unit magnets 121 of the inner magnet 21 (the unit magnets 122 in the 2nd and 4th layers in FIG. 12), and the magnetization direction is the radial direction (radial direction) and the unit magnets 121 have the opposite direction to the unit magnets 121 of the inner magnet 21 (the unit magnets 122 in the 1st, 3rd, and 5th layers in FIG. 12), and they are laminated alternately and in a direction-rotating manner (i.e., in a Halbach array). As shown in FIG. 12, by laminating the unit magnets 121 and 122 with the magnetization direction in the axial direction (the unit magnets 121 and 122 in the 2nd and 4th layers in FIG. 12) and the unit magnets 121 and 122 with the magnetization direction in the radial direction (radial direction) (the unit magnets 121 and 122 in the 1st, 3rd, and 5th layers in FIG. 12) alternately and in a direction-rotating manner (i.e., in a Halbach array), the repulsive force between the inner magnet 21 and the outer magnet 22 can be increased. Therefore, by adjusting the number of layers of the unit magnets 121 and 122, it is possible to adjust the axial rigidity and the radial rigidity of the first bearings 17a and 17b. According to the calculations of the inventors of the present case, as a first embodiment, the inner magnet 21 and the outer magnet 22 each consist of five layers of unit magnets 121 and 122 laminated alternately with the magnetization direction of the unit magnets facing downward and upward, the inner diameter of each unit magnet 121 of the inner magnet 21 is φ25 mm, the outer diameter is φ33 mm, and the thickness is 4 mm, and the inner diameter of each unit magnet 122 of the outer magnet 22 is φ41 mm, the outer diameter is φ49 mm, and the thickness is 4 mm. In this case, the radial rigidity Kr = 14 N / mm and the axial rigidity Kz = -29 N / mm.In contrast, as a second embodiment, the sizes of the unit magnets 121 of the inner magnet 21 and the unit magnets 122 of the outer magnet 22 are the same as those in the first embodiment. However, as shown in FIG. 12, when the inner magnet 21 and the outer magnet 22 are each composed of five layers of unit magnets 121 and 122 laminated such that the magnetization directions are in a Halbach array, the radial rigidity Kr = 24 N / mm and the axial rigidity Kz = -47 N / mm, and it was found that the rigidity is higher than that of the first embodiment.

[0038] According to the present embodiment as described above, since the first bearings 17a and 17b are permanent magnet type magnetic bearings, compared with the case of mechanical bearings, mechanical losses can be reduced, and the rotors 15a and 15b can be rotated at high speed. When the present inventor actually verified, as shown in FIG. 11, the first bearings 17a and 17b have five layers of unit magnets 121 and 122 in which the magnetization directions are in the same axial direction (upward in the illustrated example), the inner diameter of each unit magnet 121 of the inner magnet 21 is φ25 mm, the outer diameter is φ33 mm, and the thickness is 4 mm, and the inner diameter of each unit magnet 122 of the outer magnet 22 is φ41 mm, the outer diameter is φ49 mm, and the thickness is 4 mm. In this case, the mechanical loss is 10 W, whereas in the case of a ball bearing of the same size, the mechanical loss is 175 W. Therefore, it was found that by using permanent magnet type magnetic bearings as the first bearings 17a and 17b, the mechanical loss can be significantly reduced compared with the case of mechanical bearings.

[0039] Further, according to the present embodiment, since the first bearings 17a and 17b are permanent magnet type magnetic bearings, compared with the case of controlled magnetic bearings, electrical control of the bearings is not required and the cost is low.

[0040] Also, referring to FIGS. 1 to 5, when the vacuum pump 10 is used with the rotors 15a and 15b arranged above the motor 12, the rotating shafts 16a and 16b are subject to the downward (i.e., toward the motor 12 side) gravity. However, according to the present embodiment, due to the axial repulsive force between the inner magnet 21 and the outer magnet 22 of the first bearings 17a and 17b, the rotating shafts 16a and 16b are biased toward the second bearings 18a and 18b side (i.e., upward). Therefore, the self-weight of the rotating shafts 16a and 16b can be supported. Referring to FIG. 11, by adjusting the number of layers of the unit magnets 121 and 122 with the magnetization direction in the same axial direction, the magnitude of the upward repulsive force between the inner magnet 21 and the outer magnet 22 of the first bearings 17a and 17b may be adjusted to balance the self-weight of the rotating shafts 16a and 16b. Thereby, the movement of the rotating shafts 16a and 16b in the axial direction can be suppressed, and the rotation of the rotors 15a and 15b can be stabilized.

[0041] (Second Embodiment) Next, the second embodiment will be described. FIG. 7 is a longitudinal sectional view showing a schematic configuration of the vacuum pump 10 according to the second embodiment. FIG. 8 is a view showing a cross section taken along line D-D of the vacuum pump 10 shown in FIG. 7. FIG. 9 is a view showing a cross section taken along line E-E of the vacuum pump 10 shown in FIG. 7.

[0042] As shown in FIGS. 7 to 9, the vacuum pump 10 includes a casing 11 having a suction port and a discharge port, a motor 120, and rotors 15a and 15b disposed in the casing 11 and attached to the rotating shafts 16a and 16b of the motor 120.

[0043] Among these, the configurations of the casing 11 and the rotors 15a and 15b are the same as those in the first embodiment, and detailed description thereof will be omitted.

[0044] In this embodiment, as shown in FIGS. 7 to 9, the motor 120 is an axial-gap type motor, and includes a pair of rotating shafts 16a and 16b extending parallel to each other, a pair of rotors 230 each including a permanent magnet fixed to each of the pair of rotating shafts 16a and 16b, a pair of stators 240 each including an electromagnet arranged to face each rotor 230 in the axial direction, and a housing 20 that supports each stator 240.

[0045] Of these, one stator 240 is arranged to face the rotor 23 on the opposite side of the rotor 15a in the axial direction when viewed from the rotor 23 fixed to one rotating shaft 16a, and the other stator 240 is arranged to face the rotor 23 on the opposite side of the rotor 15b in the axial direction when viewed from the rotor 23 fixed to the other rotating shaft 16a. In the illustrated example, each rotor 230 has four magnetic poles, and each stator 240 has six slots. By controlling the current flowing through the electromagnet of each stator 240, the pair of rotating shafts 16a and 16b are rotated (reversed) in opposite directions synchronously with the rotors 15a and 15b by the magnetic force generated between the rotor 230 and the stator 240. As a result, the process gas introduced from the suction port 13 is confined in the space formed between the rotors 15a and 15b and the casing 11 and transferred to the discharge port 14 side.

[0046] As shown in FIGS. 7 to 9, the vacuum pump 10 has first bearings 17a and 17b and second bearings 18a and 18b that rotatably support the pair of rotating shafts 16a and 16b, respectively. In this embodiment, the first bearings 17a and 17b are permanent magnet type magnetic bearings, and the bearings 18a and 18b are ball bearings. The configurations of the first bearings 17a and 17b and the second bearings 18a and 18b are the same as those in the first embodiment, and detailed descriptions thereof are omitted.

[0047] As shown in FIG. 7, the inner magnets 21 of the first bearings 17a and 17b are displaced and arranged toward the second bearings 18a and 18b side (upward in FIG. 7) with respect to the outer magnets 22, and the axial repulsive force between the inner magnets 21 and the outer magnets 22 biases the rotary shafts 16a and 16b toward the second bearings 32a and 32b side (upward in FIG. 7).

[0048] According to the second embodiment as described above, in addition to obtaining the same operational effects as those of the first embodiment, during the rotation operation, the axial magnetic force generated by the axial gap type motor 120 pulls the rotary shafts 16a and 16b toward the motor 120 side (downward in FIG. 7), but the axial repulsive force between the inner magnets 21 and the outer magnets 22 of the first bearings 17a and 17b biases the rotary shafts 16a and 16b toward the second bearings 18a and 18b side (upward in FIG. 7), so that the force pulled from the motor 120 can be counteracted. Referring to FIG. 11, by adjusting the number of layers of the unit magnets 121 and 122 whose magnetization directions are the same in the axial direction, the magnitude of the upward repulsive force between the inner magnet 21 and the outer magnet 22 of the first bearings 17a and 17b may be adjusted to balance with the axial downward magnetic force generated by the axial gap type motor 120. Thereby, the movement of the rotary shafts 16a and 16b in the axial direction can be suppressed, and the rotation of the rotors 15a and 15b can be stabilized.

[0049] (Third Embodiment) Next, the third embodiment will be described. FIG. 10 is a longitudinal sectional view showing a schematic configuration of the vacuum pump 10 according to the third embodiment.

[0050] As shown in FIG. 10, the vacuum pump 10 includes a casing 11 having a suction port and a discharge port, a motor 12, rotors 15a and 15b disposed in the casing 11 and attached to the rotary shafts 16a and 16b of the motor 12, and first bearings 17a and 17b, second bearings 18a and 18b, and third bearings 19a and 19b that rotatably support the pair of rotary shafts 16a and 16b, respectively.

[0051] In the third embodiment, the configuration other than the third bearings 19a and 19b is the same as that in the first embodiment, and thus detailed description thereof is omitted.

[0052] As shown in FIG. 10, the third bearings 19a and 19b are arranged on the side opposite to the rotors 15a and 15b with respect to the motor 12, and are configured to rotatably support the ends of the rotating shafts 16a and 16b on the motor 12 side. The first bearings 17a and 17b, the second bearings 18a and 18b. In the illustrated example, the third bearings 19a and 19b are ball bearings, similar to the second bearings 18a and 18b. As an example, the inner diameter of the ball bearing may be φ4 mm, the outer diameter may be φ8 mm, the axial thickness Lg may be 2 mm, the allowable rotational speed may be 61,000 rpm, and the mechanical loss may be 20 W.

[0053] According to the third embodiment as described above, in addition to obtaining the same operational effects as those in the first embodiment, during the rotation operation, the radial magnetic force generated by the radial gap type motor 12 pulls the rotating shafts 16a and 16b in the radial direction. However, since the ends of the rotating shafts 16a and 16b on the motor 12 side can be supported by the third bearings 19a and 19b, it is possible to suppress the movement of the rotating shafts 16a and 16b in the radial direction (tilting with the second bearings 18a and 18b as the fulcrums), and the rotation of the rotors 15a and 15b can be stabilized.

[0054] (Fourth Embodiment) Next, the fourth embodiment will be described. FIG. 13 is a longitudinal sectional view showing a schematic configuration of the vacuum pump 10 according to the fourth embodiment.

[0055] As shown in FIG. 13, the vacuum pump 10 includes a casing 11 having a suction port and a discharge port, a motor 12, rotors 15a and 15b disposed in the casing 11 and attached to the rotating shafts 16a and 16b of the motor 12, and first bearings 17a and 17b and second bearings 180a and 180b that rotatably support the pair of rotating shafts 16a and 16b, respectively.

[0056] In the fourth embodiment, the configuration other than the second bearings 180a and 180b is the same as that in the second embodiment, and thus detailed description thereof is omitted.

[0057] As shown in FIG. 13, in the present embodiment, the second bearings 180a and 180b are permanent magnet type magnetic bearings, similar to the first bearings 17a and 17b, and include an inner magnet 25 formed of an annular permanent magnet fixed to the rotating shafts 16a and 16b, and an outer magnet 26 formed of an annular permanent magnet disposed radially outside the inner magnet 25 and fixed to the casing 11. In the example shown in FIG. 13, both the inner magnet 25 and the outer magnet 26 are magnetized parallel to the axial direction, but the present invention is not limited thereto, and both the inner magnet 25 and the outer magnet 26 may be magnetized in the radial direction (radial direction).

[0058] As shown in FIG. 13, the inner magnet 25 is displaced toward the first bearings 17a and 17b side (downward in FIG. 13) with respect to the outer magnet 26, and the rotating shafts 16a and 16b are biased toward the first bearings 17a and 17b side (downward in FIG. 13) by the axial repulsive force between the inner magnet 25 and the outer magnet 26. The magnitude of the downward repulsive force between the inner magnet 25 and the outer magnet 26 of the second bearings 18a and 18b may be adjusted to balance with the upward repulsive force between the inner magnet 21 and the outer magnet 22 of the first bearings 17a and 17b.

[0059] According to the fourth embodiment as described above, in addition to obtaining the same operational effects as those of the second embodiment, since the second bearings 180a and 180b are permanent magnet type magnetic bearings, mechanical losses can be further reduced as compared with the second embodiment in which the bearings are mechanical bearings, and the rotors 15a and 15b can be rotated at a higher speed.

[0060] As described above, the embodiments and modifications of the present invention have been described by way of example. However, the scope of the present invention is not limited to these, and it can be changed and modified according to the purpose within the scope described in the claims. In addition, each embodiment and modification can be appropriately combined as long as the contents do not conflict with each other.

Description of Reference Numerals

[0061] 10 Vacuum pump 11 Casing 12, 120 Motor 13 Suction port 14 Discharge port 12 Impeller 13 Rotating shaft 15a, 15b Rotor 16a, 16b Rotating shaft 17a, 17b First bearing 18a, 18b, 180a, 180b Second bearing 19a, 19b Third bearing 20 Housing 21, 25 Inner magnet 22, 26 Outer magnet 121, 122 Unit magnet 23, 230 Rotor 24, 240 Stator 31a, 31b, 32a, 32b Seal part

Claims

1. A casing having a suction port and a discharge port, a rotor disposed within the casing and attached to the rotating shaft of a motor, a first bearing disposed between the motor and the rotor and rotatably supporting the rotating shaft, a second bearing disposed on the side opposite to the motor with respect to the rotor and rotatably supporting the rotating shaft, comprising: The first bearing is a permanent magnet type magnetic bearing. A vacuum pump characterized by this.

2. The motor is a radial gap type motor. The vacuum pump according to Claim 1.

3. The motor is an axial gap type motor. The vacuum pump according to Claim 1.

4. The first bearing has an inner magnet fixed to the rotating shaft and an outer magnet disposed radially outside the inner magnet and fixed to the casing. The inner magnet is displaced toward the second bearing side with respect to the outer magnet, and the rotating shaft is biased toward the second bearing side by the axial repulsive force between the inner magnet and the outer magnet. The vacuum pump according to any one of Claims 1 to 3, characterized by this.

5. Further comprising a third bearing disposed on the side opposite to the rotor with respect to the motor and rotatably supporting the rotating shaft. The vacuum pump according to Claim 2, characterized by this.

6. The inner magnet and the outer magnet each have a plurality of unit magnets laminated in the axial direction. The vacuum pump according to any one of Claims 1 to 3, characterized by this.

7. The second bearing is a permanent magnet type magnetic bearing. The vacuum pump according to any one of Claims 1 to 3, characterized by this.

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