JPH0670440B2 - Turbo molecular pump - Google Patents

Description

TECHNICAL FIELD The present invention relates to a turbo molecular pump in which rotor blades attached to a rotor and stationary blades attached to a casing are alternately arranged in the axial direction of the rotor. .

(Prior Art) A conventional turbo molecular pump will be described with reference to FIG.
(1) is a casing, (2) is an intake port provided in the same casing (1), (3) is an exhaust port provided in the same casing (1), and (4) is a vane provided in the same casing (1). , (5)
Is a rotor blade attached to the rotor (6), and the rotor blade (5) and the stationary blades (4) are alternately arranged in the rotor shaft (7) direction of the rotor (6).

(8) is a stator arranged around the rotor shaft (7), and an upper bearing is provided between the stator (8) and the rotor shaft (7) to rotate the rotor (6) at high speed. A ball bearing (110), a ball bearing (111) as a lower bearing, and a motor (13).

The rotor shaft (7) is provided with an oil supply hole (9) for supplying the lubricating oil (112) to the ball bearings (110) (111) as upper and lower bearings. The motor (13) is composed of a cylindrical motor rotor (13a) mounted on the rotor shaft (7) and a cylindrical motor stator (13b) mounted on the stator (8). Are arranged concentrically with the rotor shaft (7).

In the above turbo molecular pump, when the rotor (6) having the rotor blade (5) and the rotor shaft (7) is rotated at high speed by the motor (13), gas molecules flow in the direction of arrow A ₁ → A ₂ The port (2) has a high vacuum and the exhaust port (3) has a low vacuum.

(Problems to be Solved by the Invention) In the conventional turbo molecular pump shown in FIG. 2, the ball bearings (110) and (111) deteriorate when operated for a long time. Therefore, it is necessary to disassemble the pumps and replace them. There is. Especially when trying to increase the speed in order to improve the exhaust performance, deterioration is remarkable in the supply and lubrication of the lubricating oil (112) through the oil supply hole (9). The lubricating oil (112)
Replenishment is necessary because it evaporates during circulation. In addition, if the operation of the turbo molecular pump is stopped after exhausting the vacuum-evacuated container, the lubricating oil (112) may be diffused back into the vacuum-exhausted container. Moreover, since the upper and lower bearings are ball bearings, vibration and noise are large,
There is a problem that the application is limited and the bearing loss is large, and the electricity cost (running cost) is high.

The present invention is proposed in view of the above problems, and the object thereof is to replace the bearings almost completely, to expand the range of application of the turbo molecular pump, to reduce the running cost, and to improve the lubricating oil. It is possible to prevent back diffusion into the vacuumed exhaust container, achieve high vacuum and ultra-high vacuum on the intake side, prevent the adverse effect on the high vacuum side cleanliness of the released gas from the permanent magnet, and ensure stable operation and rotation. The point is to provide a turbo-molecular pump that can prevent system vibration.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a rotor having a cylindrical body with a downward opening and a closed top, and a rotor shaft extending downward from the center of the top of the rotor to the inside of the rotor. And rotor blades mounted on the outer peripheral surface of the rotor and stationary blades mounted on the inner peripheral surface of the casing are alternately arranged in the axial direction of the rotor shaft, and a stator is installed around the rotor shaft in the rotor. And a lower end of the stator is fixed to the bottom of the casing, a motor rotor is attached to an upper and lower intermediate portion of the rotor shaft, and a motor is attached to an inner peripheral surface of the stator facing the motor rotor. In a turbo molecular pump with a stator attached, the upper part of the rotor shaft located on the low vacuum side in the casing is arranged above and below the permanent magnets with the polarity that attracting force acts on the rotor side and the stator side. Rotatably supported by the magnetic bearing, the upper permanent magnet on the rotor side, the lower permanent magnet on the stator side,
Each of them is attached to urge the rotor and the rotor shaft downward, and the lower part of the rotor, which is also located on the low vacuum side of the casing side, is rotatably supported by a slide bearing having load capacity in the rotor axial direction. The axial dimension from the support point of the slide bearing to the magnetic bearing is larger than the radial dimension of the magnetic bearing.

(Operation) In the turbo molecular pump of the present invention, the magnetic bearing and the sliding bearing are on the low vacuum side, and the rotor and the rotor shaft are rotatably supported by these bearings, so that gas is released from the bearing and lubricated. Solving problems such as oil evaporation, bearing replacement, lubricating oil replenishment, vibration, noise, and other problems of conventional devices are solved, but the upper part of the rotor shaft is rotatably supported by magnetic bearings. At the same time, the lower permanent magnet mounted on the stator side of the magnetic bearing attracts the upper permanent magnet mounted on the rotor side to urge the rotor and the rotor shaft downward, thereby lowering the lower part of the rotor shaft. It is rotatably supported by a sliding bearing with load capacity in the rotor axial direction, and the radial dimension is increased by increasing the axial dimension from the bearing point of the sliding bearing to the supporting bearing relative to the radial dimension of the magnetic bearing. The moment force multiplied by the axial dimension from the support point of the plain bearing to the magnetic bearing is increased, and the rotor has sufficient restoring force to hold the rotation center of the rotor, thus stabilizing the operation of the turbo molecular pump. Turn into. Further, in the magnetic bearing, the lower permanent magnet attached to the stator side attracts the upper permanent magnet attached to the rotor side to urge the rotor and the rotor shaft downward, so the weight of the rotor is light. However, a proper thrust load is applied to the slide bearing, and the spring and damping in the direction perpendicular to the axis of the magnetic bearing can be largely taken, and vibration of the rotary system can be prevented.

(Example) Next, the turbo molecular pump of the present invention will be described with reference to an example shown in Fig. 1. (1) is a casing, (2) is an intake port provided in the casing (1), and (3) is An exhaust port provided in the casing (1), a vane (4) provided in the casing (1), a cylindrical rotor (6) having a downward opening and a top closed, and (5) Same rotor (6)
A rotor blade (7) attached to the rotor (6) is a rotor shaft (rotating shaft) vertically extending downward from the center position of the top of the rotor (6) to the rotor blade (5) and the stator blade (4). ) Are alternately arranged in the direction of the rotor shaft (7), and the rotor shaft (7) is located on the low vacuum side in the casing (1).

(8) is a stator arranged around the same rotor shaft (7),
(10) is a magnetic bearing that supports the top of the rotor (6) so that it can rotate at high speed, and (11) is a slide bearing that supports the bottom of the rotor shaft (7) that can rotate at high speed.
Are arranged between the top of the rotor (6) and the top of the stator (8). Reference numeral (11) is a slide bearing (11) that rotatably supports the lower portion of the rotor shaft (7), and the slide bearing (11) is arranged on the bottom of the casing (1) in the lower portion of the stator (8). There is.

The above magnetic bearing (10) is composed of an upper permanent magnet (10a) and a lower permanent magnet (10b) which is arranged opposite to the upper permanent magnet (10a) with a polarity that an attractive force acts on the upper permanent magnet (10a). One permanent magnet (10a) is attached to the top of the rotor (6), and the lower magnetic bearing (10b) is attached to the upper part of the stator (8) so that the rotor (6) and the rotor shaft (7) are Even if the rotor (6) is light in weight because it is biased downward (in the direction of the slide bearing (11)), the spring and damping in the direction perpendicular to the axis of the magnetic bearing (10) can be largely removed, and vibration of the rotating system Is being stabilized.

The slide bearing (11) includes a rotating shaft (11a) mounted on the lower end of the rotor shaft (7) of the rotor (6) and a bearing disc (11b) held by a bearing support member (15). The tip of the rotating shaft (11a) and the bearing plate (11b) are lubricated with oil (12).
Configured to contact through this plain bearing (1
In 1), a dynamic pressure type bearing such as a spiral group bearing having a load capacity in the axial direction and the direction perpendicular to the rotor (6) and the rotor shaft (7) is used.

The axial dimension from the support point of the slide bearing (11) to the magnetic bearing (10) is larger than the radial dimension of the magnetic bearing (10).

As the lubricating oil (12), one having an extremely small evaporation amount (generally having a high viscosity) is used.

Next, the operation of the turbo molecular pump shown in FIG. 1 will be specifically described.

Of the magnetic bearing (10), the permanent magnet (10
a) is upward and the permanent magnet (10b) on the stator (8) side is downward, and the rotor (6) and the rotor shaft (7) are attached downward (in the direction of the slide bearing (11)). It is energized. In this magnetic bearing (10), the permanent magnet (10a) on the rotor (6) side and the permanent magnet (10b) on the stator (8) side
And the magnetic center of the rotor (6) are concentric with each other, the rotational center of the rotor (6) is concentric with the axial center of the stator (8), and the magnetic bearing (10) with respect to the rotor (6) and the rotor shaft (7). Function as an upper bearing.

On the other hand, a slide bearing (11) is arranged immediately below the rotor shaft (7). In this slide bearing (11), the bearing disc (11b) is held concentrically with the shaft center of the stator (8) by the bearing support member (15) to provide an appropriate spring and damping, and the rotor in the axial direction. It has a load capacity against the load of (6) and the like, and has a load capacity against rotational vibration in the direction perpendicular to the axis.

A groove (for example, a spiral groove) is provided at the tip of the rotary shaft (11a) of the slide bearing (11), and this groove is rotated from the lower portion of the stator (8) by the rotation of the rotary shaft (11a). The lubricating oil (12) is smoothly introduced into the (11b) to maintain the load capacity of the slide bearing (11), and the slide bearing (11) including the bearing disc (11b) is the rotor (6) and the rotor. It functions as a lower bearing for the shaft (7).

Moreover, the axial dimension from the support point of the slide bearing (11) to the magnetic bearing (10) is made larger than the radial dimension of the magnetic bearing (10). Therefore, the radial force and the support of the slide bearing (11) are increased. The moment force multiplied by the axial dimension from the point to the magnetic bearing (10) becomes large, and a sufficient restoring force acts on the rotor (6) to hold the rotation center of the rotor (6). Pump movement is stabilized.

(Effects of the Invention) The turbo molecular pump of the present invention is configured as described above, and can achieve the following effects. In other words, since the magnetic bearing (upper bearing) is not in contact, the upper bearing does not deteriorate, and the sliding bearing (lower bearing) does not deteriorate in normal operating conditions. The frequency of replacement is much smaller than that of ball bearings, and therefore replacement of the bearings can be made almost unnecessary.

Vibration and noise are very small, it can be used in places where vibration is disliked, and the range of application of turbo molecular pumps can be expanded.

Bearing loss can be reduced and running cost can be reduced.

Since it is not necessary to circulate the lubricating oil, it is possible to use high-viscosity lubricating oil, that is, lubricating oil with a very small evaporation amount, and it is possible to almost eliminate the need to replenish the lubricating oil. Diffusion can be prevented.

All components that easily adsorb gas, such as magnetic bearings (upper bearings) and sliding bearings (lower bearings), can be placed inside the rotor on the exhaust side (low vacuum side), and high vacuum, ultra-high vacuum on the intake side Can be achieved.

The magnetic bearing can be arranged in the rotor on the exhaust side (low vacuum side), and the adverse effect of the gas released from the permanent magnet on the cleanliness on the high vacuum side can be prevented.

By increasing the axial dimension from the slide bearing support point to the magnetic bearing relative to the radial dimension of the magnetic bearing, the moment force obtained by multiplying the radial force by the axial dimension from the slide bearing support point to the magnetic bearing. Is increased, a sufficient restoring force acts on the rotor, and the center of rotation of the rotor is held, so that the operation of the turbo molecular pump can be stabilized.

Of the magnetic bearings, the lower permanent magnet mounted on the stator side attracts the upper permanent magnet mounted on the rotor side to urge the rotor and rotor shaft downward, so even if the rotor is light in weight. Since an appropriate thrust load is applied to the slide bearing, the spring and the doping of the magnetic bearing in the direction perpendicular to the axis can be largely taken, and the vibration of the rotary system can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical side view showing an embodiment of a turbo molecular pump of the present invention, and FIG. 2 is a vertical side view showing a conventional turbo molecular pump. (1) ...... Casing, (4) ...... Static blade, (5) ...... Roller blade, (6) ...... Rotor, (7) ...... Rotor shaft (rotating shaft), (8) ...... Stator, ( 10) …… Magnetic bearing, (10
a) ... Permanent magnet on the rotor (6) side, (10b) ... Permanent magnet on the stator (8) side, (11) ... Plain bearing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akemi Kaneko 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Shipyard (56) Reference JP-A-59-162396 (JP, A) ) JP-A-58-79695 (JP, A) JP-A-59-168295 (JP, A)

Claims (1)

[Claims] Claim: What is claimed is: 1. A rotor having a cylindrical body with a downward opening and a closed top, a rotor shaft extending vertically downward from the center of the top of the rotor, and attached to the outer peripheral surface of the rotor. The stator vanes attached to the inner peripheral surface of the casing are arranged alternately in the axial direction of the rotor shaft, the stator is arranged around the rotor shaft in the rotor, and the lower end of the stator is the bottom of the casing. In the turbo molecular pump in which the motor rotor is attached to the upper and lower intermediate portions of the rotor shaft, and the motor stator is attached to the inner peripheral surface of the stator facing the motor rotor, the low vacuum side in the casing Rotatably supporting the upper portion of the rotor shaft located at a rotor side and a stator side by magnetic bearings composed of permanent magnets that are vertically opposed to each other with the polarity of the attraction force acting,
Of the same magnetic bearing, the upper permanent magnet is attached to the rotor side and the lower permanent magnet is attached to the stator side to urge the rotor and the rotor shaft downward, and are also located on the low vacuum side of the casing side. The lower part on the rotor side is rotatably supported by a sliding bearing with load capacity in the rotor axial direction,
A turbo-molecular pump, wherein an axial dimension from a support point of the slide bearing to the magnetic bearing is made larger than a radial dimension of the magnetic bearing.