JP2017025868A - Vacuum pump device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum pump device which can exhibit excellent energy efficiency, and can be easily manufactured, and which can achieve high rotation speed and miniaturization.SOLUTION: A vacuum pump device evacuates gas by rotating a pump rotor. The vacuum pump device includes a main shaft for outputting rotational power to the pump rotor, a motor rotor attached to the main shaft, and a motor stater confronting the motor rotor in an axial direction of the main shaft. The motor stater includes a plurality of cores formed at equal intervals in a circumferential direction and protruding to the axial direction of the main shaft, a supporting part separately provided from the cores and supporting the cores by being fixed with the cores, and a stator coil wound around the cores. The cores are formed by laminating band-like amorphous metal, and is arranged in such a manner that a width direction of the band-like amorphous metal is along the axial direction of the main shaft.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a vacuum pump device.

  Conventionally, a vacuum pump apparatus is used for exhausting a process gas in a vacuum chamber in which, for example, a semiconductor manufacturing apparatus is disposed. Generally, in a semiconductor manufacturing process, the inside of a vacuum chamber is required to be a clean atmosphere. For this reason, a dry vacuum pump that does not use oil in a gas flow path inside the pump is used as a vacuum pump device. As such a dry vacuum pump, for example, a biaxial root type multistage positive displacement dry vacuum pump is known.

  The biaxial root type multistage positive displacement dry vacuum pump includes a pair of opposed roots type multistage rotors in a casing, and clearance is provided so that a gap between these rotors and between the rotor and the casing is very small. . Then, when the pair of rotors are synchronously inverted, the process gas is confined in the space formed between the rotor and the casing and transferred to the subsequent stage. In the multistage positive displacement dry vacuum pump, the process gas is exhausted by continuously performing this transfer.

  The vacuum pump is provided with a motor that rotationally drives the rotor of the vacuum pump. Generally, in a vacuum pump, reduction of power consumption is an issue, and conventionally, for example, by reducing heat generation of a motor rotor, a reduction in energy efficiency of the vacuum pump is suppressed.

JP-A-2005-61421

  In the vacuum pump device, the output of the motor is determined on the basis of a high load, for example, when a large amount of process gas is generated in the vacuum chamber so that a desired pump performance can be achieved. However, the vacuum pump device is often driven with a low load. In such a case, the efficiency of the motor may be deteriorated.

  Losses that reduce the efficiency of the motor include iron losses such as eddy current loss caused by rotation of the motor rotor, and copper loss generated as Joule heat from the current flowing in the coil, excluding mechanical loss. . When the load is low, the current flowing through the coil is small, so the copper loss is small. However, the iron loss increases depending on the rotation speed of the motor rotor regardless of the magnitude of the load. The configuration of the motor rotor and the motor stator is related to the output of the motor, and is determined based on a large load. Therefore, especially when the motor is driven at a low load and a high rotational speed, the influence of the iron loss increases and the motor Energy efficiency gets worse.

  Conventionally, a motor having a can structure or the like is used as a motor of a vacuum pump device. However, when a motor having a can structure or the like is used, the vacuum pump has an overhang (cantilever) structure, which is not suitable for increasing the number of rotations and reducing the size. Further, in general, it is desired that the vacuum pump device can be easily manufactured.

The present invention has been made in order to solve at least a part of the above-described problems, and an object of the present invention is to provide a vacuum pump device that can be easily manufactured with high energy efficiency. Another object of the present invention is to provide a vacuum pump device capable of increasing the number of rotations and reducing the size.

  The vacuum pump device of the present invention is a vacuum pump that evacuates gas by rotating a pump rotor. The vacuum pump device includes a main shaft for outputting rotational power to the pump rotor, a motor rotor attached to the main shaft, and a motor stator arranged to face the motor rotor in the axial direction of the main shaft. The motor stator has a plurality of core portions arranged at equal intervals in the circumferential direction and projecting in the axial direction of the main shaft, and the plurality of core portions are provided separately and fixed to the plurality of core portions. And a stator coil wound around the plurality of core portions. The plurality of core portions are formed by laminating strip-shaped amorphous metals, and are arranged such that the width direction of the strip-shaped amorphous metal is along the axial direction of the main axis.

  With this configuration, since the core portion is formed by laminating amorphous metal having a lower electric resistance than that of a general silicon steel plate, iron loss can be reduced. Moreover, since the stator is formed with the core portions arranged at equal intervals in the circumferential direction and the support portions that support the plurality of core portions, the stator can be easily formed. Therefore, with this configuration, it is possible to provide a vacuum pump device that can be easily manufactured with high energy efficiency. Further, since the motor rotor and the motor stator are provided so as to face each other in the rotation axis direction, it is possible to increase the number of rotations and reduce the size of the vacuum pump device.

Further, the plurality of core portions may be formed by laminating strip-shaped amorphous metal in a direction perpendicular to the axial direction of the main axis. In this case, the plurality of core portions may be formed by cutting a ring-shaped or disk-shaped member formed by winding a strip-shaped amorphous metal into a plurality.
By doing so, the core portion is formed by laminating the amorphous metal in the radial direction, so that the iron loss can be reduced.

Further, the plurality of core portions may be formed by winding a strip-shaped amorphous metal in a cylindrical shape.
By so doing, the core portion is formed by laminating amorphous metal in the direction connecting the center of the core portion and the rotation center of the main shaft, so that the iron loss can be reduced.

The motor rotor may include a first motor rotor and a second motor rotor, and the motor stator may be disposed between the first motor rotor and the second motor rotor in the axial direction of the main shaft. The core portion may be fixed to a surface of the support portion that faces the first motor rotor and a surface that faces the second motor rotor.
In this way, the vacuum pump device can be further improved in efficiency and size.

The stator coil may be formed by winding a coil member.
If it carries out like this, the clearance gap when a stator coil is arrange | positioned in a groove part can be made small, and the improvement of the energy efficiency of a vacuum pump apparatus can be aimed at.

Further, the vacuum pump may have a pair of pump rotors arranged in parallel and rotating synchronously as pump rotors.
Further, the vacuum pump may be a multistage positive displacement type in which a pair of pump rotors has a multistage rotor.

It is sectional drawing which shows schematic structure of the vacuum pump apparatus of this embodiment. It is other sectional drawing which shows schematic structure of the vacuum pump apparatus of this embodiment. It is sectional drawing which shows schematic structure of the motor of this embodiment. It is a figure which shows schematic structure of the stator core used for the motor of this embodiment. It is a figure which shows an example of the process in which the stator core of this embodiment is manufactured. It is a figure which shows an example of the process in which the stator core of this embodiment is manufactured. It is a figure which shows an example of the stator coil of this embodiment. It is a figure which shows the exhaust speed (L / M) with respect to the suction side pressure (Pa) in a common vacuum pump apparatus, and power consumption (W). It is a figure which shows the efficiency (evacuation speed performance) of the vacuum pump apparatus with respect to power consumption (W). It is a figure which shows schematic structure of the stator core of a modification. It is sectional drawing which shows schematic structure of the motor of a modification.

  Hereinafter, a vacuum pump device according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted. The vacuum pump apparatus of this embodiment is comprised as a multistage positive displacement pump, and can be utilized as one of manufacturing equipment, such as a semiconductor, a liquid crystal, a solar panel, or LED, for example.

  FIG. 1 is a cross-sectional view showing a schematic configuration of the vacuum pump device of the present embodiment. FIG. 1 shows a cross section including the rotation center axis AR1 of one pump rotor 310 of the pair of pump rotors 310, 410 included in the vacuum pump device 100. FIG. 2 is another cross-sectional view showing a schematic configuration of the vacuum pump device of the present embodiment. FIG. 2 shows a cross section including the rotation center axes AR1 and AR2 of both the pair of pump rotors 310 and 410 included in the vacuum pump device 100.

  As shown in FIGS. 1 and 2, the vacuum pump device 100 includes a motor 200, a pair of pump main shafts 300 and 400 that are rotationally driven by the motor 200, and a pair of pump rotors 310 that rotate integrally with the pump main shafts 300 and 400. , 410. In FIG. 1, only one pump main shaft 300 and pump rotor 310 are shown.

  The pair of pump rotors 310 and 410 constitutes a multistage compression stage. As an example, the pump rotor 310 includes first to fifth stage pump rotors 311 to 315 attached to the pump main shaft 300 at intervals. The pump rotor 410 includes first to fifth stage pump rotors 411 to 415 attached to the pump main shaft 400 at intervals.

  The first to fifth stage pump rotors 311 to 315 and 411 to 415 are accommodated in a space formed by the upper casing 320 and the lower casing 330. An upper closing plate 322 is attached to the upper portion of the upper casing 320, and a lower closing plate 332 is attached to the lower portion of the lower casing 330.

  The upper closing plate 322 is formed with an intake port 324 for sucking processing gas into the pump rotors 310 and 410. The lower closing plate 332 is formed with an exhaust port 334 for exhausting the processing gas from the pump rotors 310 and 410.

An exhaust-side intermediate member that accommodates the pump main shafts 300 and 400 protruding toward the counter-motor 200 is provided on the counter-motor 200 side (the side far from the motor 200, the right side in FIGS. 1 and 2) of the upper casing 320 and the lower casing 330. 360 is provided. Further, an exhaust side cover 370 is provided on the side of the exhaust side intermediate member 360 opposite to the motor 200. The exhaust side intermediate member 360 and the exhaust side cover 370 are connected to the anti-motor 2 from the upper casing 320 and the lower casing 330.
The pump main shafts 300 and 400 protruding toward the 00 side are accommodated. The pump main shafts 300 and 400 are pivotally supported by bearings 342 and 442 in a portion protruding from the space formed by the upper casing 320 and the lower casing 330 to the side opposite to the motor 200. The bearings 342 and 442 are accommodated in the exhaust side intermediate member 360 and the exhaust side cover 370. In addition, a pair of timing gears 380 and 480 are accommodated in the exhaust side cover 370. The timing gears 380 and 480 are connected to the pump main shafts 300 and 400 and mesh with each other.

  The exhaust-side intermediate member 360 has a groove formed in a circumferential direction on a surface facing the pump main shafts 300 and 400, and includes the groove between the exhaust-side intermediate member 360 and the pump main shafts 300 and 400. Intermediate chambers 362 and 462 are provided. The intermediate chambers 362 and 462 and the exhaust port 334 are communicated with each other through a communication path 364.

  On the motor 200 side (left side in FIGS. 1 and 2) of the upper casing 320 and the lower casing 330, an intake-side intermediate member 345 that houses the pump main shafts 300 and 400 protruding toward the motor 200 is provided. The intake side intermediate member 345 accommodates the pump main shafts 300 and 400 protruding from the upper casing 320 and the lower casing 330 to the motor 200 side. The pump main shaft 300 is pivotally supported by a bearing 340 accommodated in the intake side intermediate member 345, and an end portion of the pump main shaft 300 is connected to the motor 200. The pump main shaft 400 is pivotally supported by a bearing 440 accommodated in the intake side intermediate member 345, and the end of the pump main shaft 400 is accommodated in the side cap 450.

  When the motor 200 is driven, the pump main shaft 300, the pump rotor 310, and the timing gear 380 are rotationally driven. As the timing gears 380 and 480 mesh with each other, the pump main shaft 400 and the pump rotor 410 are also rotationally driven. The pair of pump rotors 310 and 410 has a slight gap between the inner surfaces of the upper casing 320 and the lower casing 330 and between the first to fifth stage pump rotors 311 to 315 and 411 to 415, Synchronously rotates in the opposite direction without contact. As the pair of pump rotors 310 and 410 rotate, the processing gas introduced from the intake port 324 is compressed and transferred by the first to fifth stage pump rotors 311 to 315 and 411 to 415 and discharged from the exhaust port 334. The

  Next, the configuration of the motor 200 will be described. FIG. 3 is a cross-sectional view showing a schematic configuration of the motor of the present embodiment. The motor 200 is used as a rotational drive source of the vacuum pump device 100 (pump rotor 310). The motor 200 includes a motor frame 250, a motor rotor 220 provided on the pump main shaft 300, and a motor stator 230 fixed to the motor frame 250. As illustrated, the motor 200 is configured as a so-called axial gap type motor in which a motor rotor 220 and a motor stator 230 face each other in the direction of the rotation center axis AR1 of the pump main shaft 300.

  The motor rotor 220 is directly connected to the pump main shaft 300 and includes a permanent magnet 222. The motor frame 250 includes a frame main body 252 and a stator support portion 254. The frame main body 252 is formed in a bottomed cylindrical shape in which an internal space is formed along the rotation center axis AR1. The stator support portion 254 is formed in a disk shape and is disposed inside the frame body 252. Stator support 254 separates the internal space of frame body 252 into a rotor chamber in which motor rotor 220 is disposed and a stator chamber in which motor stator 230 is disposed.

The motor stator 230 has a configuration in which a stator coil 236 is mounted on a stator core 232. The motor stator 230 is fixed to the frame body 252 concentrically with the rotation center axis AR <b> 1 via the stator support portion 254 by attaching the stator core 232 to the stator support portion 254.

  FIG. 4 is a diagram showing a schematic configuration of a stator core used in the motor of the present embodiment. As illustrated, the stator core 232 supports a plurality of core portions 233 by being fixed to a plurality of (for example, six, twelve, etc.) core portions 233 facing the permanent magnet 222 of the motor rotor 220 and the plurality of core portions 233. And a support portion 234. The plurality of core portions 233 protrude in the direction of the rotation center axis AR1 and are arranged at equal intervals in the circumferential direction. A stator coil 236 is wound around each of the plurality of core portions 233.

  5 and 6 are diagrams showing an example of a process for manufacturing the stator core of the present embodiment. In the stator core 232 of the present embodiment, the core portion 233 is formed of an amorphous (amorphous) metal. As an example of the amorphous metal, a material mainly composed of a ferromagnetic metal such as iron, nickel, or cobalt can be used. Generally, an amorphous metal is formed into a thin foil by forming an amorphous body by rapid cooling. A strip-shaped amorphous metal 500 is prepared using the foil-shaped amorphous metal. The band-shaped amorphous metal 500 has a cross section having a width Ws and a thickness Ts, and the width Ws is larger than the thickness Ts. Here, the strip-shaped amorphous metal 500 preferably has a width Ws equal to the thickness (length in the direction of the rotation center axis AR1) Hs of the core portion 233 (see FIGS. 4 and 5). Note that the thickness Hs of the core portion 233 may be determined based on the rated output of the motor 200 or the like.

  Then, as shown in FIG. 5, a strip-shaped amorphous metal 500 is spirally wound around a winding frame 510 such as a cylindrical body to produce an air-core cylindrical amorphous metal body 520. When the outer diameter of the amorphous metal body 520 reaches a desired size (outer diameter of the stator core 233) by winding the strip-shaped amorphous metal 500, the amorphous metal body 520 is removed from the winding frame 510. Here, the shape of the amorphous metal body 520 may be fixed by using heating and cooling, bonding, or the like while winding the band-shaped amorphous metal 500 around the winding frame 510. Further, after reaching a desired outer diameter, the shape may be fixed by applying a film to the outer edge of the amorphous metal body 520 or the like. In the amorphous metal body 520 thus formed, the amorphous metal is laminated in the radial direction (in the direction of the straight line AC perpendicular to the rotation center axis AR1, see FIG. 6).

  Subsequently, the plurality of core portions 233 are formed by cutting the amorphous metal body 520 into a plurality of pieces. As an example, the plurality of core portions 233 are formed by cutting the amorphous metal body 520 radially at equal angles. The core portion 233 thus formed has a structure in which the width direction Aw of the strip-shaped amorphous metal 520 is arranged along the rotation center axis AR1, and the amorphous metal is laminated in the radial direction. Then, as shown in FIG. 6, the stator core 232 is manufactured by fixing the plurality of core portions 233 to the support portion 234. Here, as an example, the support portion 234 may be formed in a ring shape or a disk shape by winding a band-shaped amorphous metal around the winding frame 510, similarly to the amorphous metal body 520. However, the support portion 234 is not limited to being formed of an amorphous metal, and may be formed of another metal. The core part 233 and the support part 234 can be fixed by, for example, adhesion using an adhesive or welding using a filler material. The core part 233 and the support part 234 may be fixed by fastening using screws or the like.

By separately forming the core portion 233 and the support portion 234 in this manner, the stator core 232 is compared with a case where, for example, a part of the amorphous metal body 520 is cut to form a groove portion and a convex portion (core portion). Can be easily manufactured. Further, when the stator core 232 is manufactured by cutting a part of the amorphous metal body 520, the cut amorphous metal cannot be used as the stator core 232. On the other hand, in the present embodiment, the amorphous metal body 520 is radially cut to form a plurality of core portions 233, so that the remaining amorphous metal body 520 is used as the core portion 233 of another stator core 232. be able to. Therefore, the manufacturing cost of the stator core 232 can be reduced.

  FIG. 7 is a diagram illustrating an example of the stator coil of the present embodiment. As shown in the figure, the stator coil 236 of the present embodiment is formed by winding a strip-shaped coil member having a width Wc equal to the height Hs of the core portion 233 around the core portion 233 of the stator core 232 in a spiral shape. Yes. The band-shaped coil member has a cross section having a width Wc and a thickness Tc, and the width Wc is larger than the thickness Tc. However, the width Wc of the coil member forming the stator coil 236 may be smaller than the height Hs of the core portion 233. The strip-shaped coil member is wound around the core 233 so that the width direction thereof is along the rotation center axis AR1. Note that the coil member 327 for drawing may be connected to the end portion on the inner peripheral side of the stator coil 236 by soldering or the like. In this manner, the strip-shaped coil member is wound around the core portion 233 to form the stator coil 236, so that the stator coil 236 is inserted into the groove portion 234 of the stator core 232 as compared with the case where the linear coil member is wound. It can be arranged without a gap. Thereby, high performance and miniaturization of the motor 200 can be achieved.

  FIG. 8 is a diagram showing an exhaust speed (L / M) and power consumption (W) with respect to an intake side pressure (Pa) in a general vacuum pump device. In general, in the vacuum pump device, when the intake side pressure is large, the load of the pump rotor that compresses the gas increases, and the power consumption increases and the exhaust speed decreases. And in a vacuum pump apparatus, the structure of an apparatus is determined on the basis of the time of high load so that desired exhaust performance can be implement | achieved also at the time of high load. However, when the vacuum pump device is provided in a semiconductor manufacturing process, it is not always driven in a high load environment, but is often driven in a low load environment. That is, the vacuum pump device is often operated in an environment with low power consumption.

  FIG. 9 is a diagram showing the efficiency (evacuation speed performance) of the vacuum pump device with respect to power consumption (W). In FIG. 9, the solid line shows the vacuum pump device of the present embodiment, and the broken line shows the vacuum pump device of the comparative example in which the stator core is formed of a general silicon steel plate. In the vacuum pump device 100 of the present embodiment, the core portion 233 of the stator core 232 is formed of an amorphous metal having an electric resistance smaller than that of a general silicon steel plate, so that the iron loss of the motor 200 can be reduced. For this reason, as shown in FIG. 9, in the vacuum pump apparatus 100 of this embodiment, compared with a comparative example, efficiency when especially power consumption is small can be made high. Thereby, energy efficiency when the vacuum pump device is operated at a low load can be improved, and a highly efficient vacuum pump device can be realized.

  In the vacuum pump device 100 of the present embodiment described above, the amorphous metal body 520 is formed by laminating amorphous metal in the radial direction. A plurality of core portions 233 are formed by cutting the amorphous metal body 522 into a plurality of pieces. The stator core 232 of the motor 200 is formed by fixing the plurality of core portions 233 to the support portion 234. In this way, the stator core 232 can be easily manufactured by forming the stator core 232 by forming the plurality of core portions 233 and the support portions 234 respectively. Moreover, since the core part 233 of the stator core 232 is formed by laminating amorphous metals in the radial direction, the iron loss of the motor 200 can be reduced. Furthermore, in the vacuum pump device 100 of the present embodiment, the motor rotor 220 and the motor stator 230 are provided facing the rotation center axis AR1, so that the vacuum pump device 100 can be increased in speed and size. it can.

(Modification 1)
In the embodiment described above, the core portion 233 is formed by radially cutting the amorphous metal body 520 formed by winding the band-shaped amorphous metal 500. However, a core formed by winding a strip-shaped amorphous metal 500 into a cylindrical shape may be used as the core portion 233. FIG. 10 is a diagram showing a schematic configuration of a modified stator core. As shown in the drawing, in the stator core 232A of the modified example, a plurality of core portions 233A are formed by winding a strip-shaped amorphous metal 500 in a columnar shape. The plurality of core portions 233A configured in this manner has a structure in which the width direction Aw of the strip-shaped amorphous metal 500 is arranged along the rotation center axis AR1. The core portion 233A has a structure in which an amorphous metal 500 is stacked in a direction AC connecting the center of the core portion 233A and the rotation center axis AR1. Also in the stator core 232A of the modified example configured as described above, the iron loss of the motor 200 can be reduced.

(Modification 2)
In the above-described embodiment, the motor 200 has a set of the motor rotor 220 and the motor stator 230. However, the motor 200 may include two or more of at least one of the motor rotor 220 and the motor stator 230. FIG. 11 is a cross-sectional view showing a schematic configuration of a modified motor. In the modified motor 200A, the pump main shaft 300 is provided to penetrate the stator support 253 and the motor stator 230A, and the two motor rotors 220A and 220B are attached to the pump main shaft 300 so as to sandwich the motor stator 230A. Yes. The stator core 232 of the motor stator 230A is provided with a core portion 233 on both end faces in the direction of the rotation center axis AR1, and a stator coil 236 is wound thereon. With such a configuration, it is possible to improve the performance of the motor 200 and to reduce the size of the motor 200 in the radial direction. Further, by sandwiching the motor stator 230 between the two motor rotors 220A and 220B, the pump main shaft 300 can be prevented from being biased in one direction of the rotation center axis AR1 when the motor 200 is driven. The main shaft 300 can be rotated stably. The motor 200 may be configured such that the motor rotor 220 is sandwiched between the motor stators 230 instead of or in addition to the motor stator 230 sandwiched between the motor rotors 220.

  Although the embodiments of the present invention have been described above, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof. In addition, any combination of the embodiment and the modified example is possible within a range where at least a part of the above-described problems can be solved or a range where at least a part of the effect can be achieved, and is described in the claims and the specification. Any combination or omission of each component is possible.

DESCRIPTION OF SYMBOLS 100 Vacuum pump apparatus 200 Motor 220,220A, 220B Motor rotor 230,230A Motor stator 232,232A Stator core 233,233A Core part 234 Support part 236 Stator coil 300,400 Pump main shaft 310,410 Pump rotor

Claims (8)

A vacuum pump device that evacuates gas by rotating a pump rotor,
A main shaft for outputting rotational power to the pump rotor;
A motor rotor attached to the main shaft;
A motor stator disposed opposite to the motor rotor in the axial direction of the main shaft;
With
The motor stator is arranged at equal intervals in the circumferential direction and protrudes in the axial direction of the main shaft, and the plurality of core parts are provided separately and fixed to the plurality of core parts. A support portion for supporting the plurality of core portions, and a stator coil wound around the plurality of core portions,
The plurality of core portions are formed by laminating a band-shaped amorphous metal, and are arranged so that a width direction of the band-shaped amorphous metal is along an axial direction of the main axis.
Vacuum pump device. The vacuum pump device according to claim 1,
The plurality of core portions are formed by laminating the strip-shaped amorphous metal in a direction perpendicular to the axial direction of the main shaft,
Vacuum pump device. The vacuum pump device according to claim 2,
The plurality of core parts are formed by cutting an annular or disk-shaped member formed by winding the band-shaped amorphous metal into a plurality of parts,
Vacuum pump device. The vacuum pump device according to claim 1,
The plurality of core portions are formed by winding the strip-shaped amorphous metal into a columnar shape,
Vacuum pump device. The vacuum pump device according to any one of claims 1 to 4,
The motor rotor has a first motor rotor and a second motor rotor,
The motor stator is disposed between the first motor rotor and the second motor rotor in the axial direction of the main shaft,
The core portion is fixed to a surface of the support portion that faces the first motor rotor and a surface that faces the second motor rotor.
Vacuum pump device. A vacuum pump device according to any one of claims 1 to 5,
The stator coil is formed by winding a strip-shaped coil member.
Vacuum pump device. The vacuum pump device according to any one of claims 1 to 6,
The pump rotor has a pair of pump rotors arranged in parallel and rotating synchronously,
Vacuum pump device. The vacuum pump device according to claim 7,
The pair of pump rotors is a multistage positive displacement type having a multistage rotor.
Vacuum pump device.

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