JP2001295843A - Static pressure gas bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a static pressure gas bearing generating no discharge in a bearing clearance in the static pressure gas bearing used in vacuum and limiting the bearing clearance by generating an electrostatic attracting force between a moving element and a guide. SOLUTION: An electrostatic attracting means is arranged only in a position corresponding to a part where a pressure of a floating gas is sufficiently low in the bearing clearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic gas bearing used in a vacuum.

[0002]

2. Description of the Related Art It is required that a bearing gap of a hydrostatic gas bearing used in a vacuum is limited to a certain height in order to secure sealing performance and bearing performance. Conventionally, a method has been adopted in which a voltage is applied between a guide and a moving body to generate an electrostatic attractive force, and the attractive force is controlled to limit a bearing gap.

[0003]

In order to limit the clearance between the bearings by electrostatic attraction, it is necessary to apply a high voltage of several hundreds to several kV between the guide and the moving body. However, when the high voltage is applied to a distance of about 5 μm, which is the floating gap of the bearing, in an atmosphere of atmospheric pressure or higher, a discharge phenomenon occurs between the electrodes, and not only the required electrostatic attraction force cannot be obtained, but also the damage of the parts. And other serious problems.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a static pressure gas bearing which generates an electrostatic attraction between a moving body and a guide to limit a bearing gap. Another object of the present invention is to provide a hydrostatic gas bearing in which no discharge occurs in a bearing gap.

[0005]

According to the present invention, there is provided a static pressure gas bearing comprising a guide having a guide surface and a moving body moving on the guide surface. In a static pressure gas bearing having an electrostatic suction means for mutually attracting, the electrostatic suction means is arranged only in a portion where the pressure of the floating gas is sufficiently low.

By this means, it is possible to provide a static pressure gas bearing which prevents a discharge phenomenon when an attraction voltage is applied to the bearing floating gap and operates safely.

In a preferred embodiment of the present invention, the electrostatic suction means is preferably arranged so as to avoid the static pressure pad portion and the air opening groove.

In a preferred embodiment of the present invention, the electrostatic suction means may be arranged so as to avoid the static pressure pad portion, the open air groove portion and the labyrinth portion.

In a preferred embodiment of the present invention, the electrostatic suction means may be formed integrally with the moving body or the guide.

In a preferred aspect of the present invention, a dimension between an electrode gap formed between the electrostatic suction means provided on the moving body and the electrostatic suction means provided on the guide is set to be equal to an air pad portion. It is good to design it so that it differs from the dimension of the floating gap.

[0011]

FIG. 1 is a sectional view of a hydrostatic gas bearing for vacuum according to an embodiment of the present invention. In FIG. 1, the guide 2 is made of a dielectric material, has a static pressure pad 7 at the center, and has an internal electrode 5 for electrostatic suction formed inside. The electrode terminal 3 is for applying a voltage to the internal electrode 5 of the guide 2, and the internal electric wire 4 is for transmitting the voltage applied to the electrode terminal 3 to the internal electrode 5.
The moving body 1 is made of ceramic and has an internal electrode 5 of the guide 2.
The metal plate 13 is arranged at a position facing the. An electric wire 14 is connected to the metal plate 13 and grounded. Metal plate 1
3 by applying a potential difference between the internal electrode 5 and the moving body 1.
And the guide 2 can generate an electrostatic attraction force. 6 is a bearing gap. Reference numeral 8 denotes an airway for supplying a floating gas to the static pressure pad 7.

Reference numeral 9 denotes a moving body 1 surrounding the static pressure pad section 7.
Open air groove formed above. Reference numeral 10 denotes an atmosphere opening hole connecting the atmosphere opening groove 9 to the atmosphere outside the chamber. Reference numeral 11 denotes a double pocket formed on the moving body 1 so as to surround the air opening groove 9. Reference numeral 12 denotes an exhaust hole for exhausting the pocket 11 by a pump.

A labyrinth portion (a structure in which the space between the air opening groove 9 and each pocket 11 serves as a barrier to prevent gas release to the outside) including the air opening groove 9 and the pocket 11, the air opening hole 10, the exhaust hole 12 and Since the fluid exhaust mechanism is constituted by a rotary pump (not shown) connected to the exhaust hole 12, most of the gas supplied to the bearing is exhausted by this mechanism. For this reason, a small amount of gas flows out into the vacuum chamber, and the static pressure gas bearing can be used in a vacuum. In addition, by disposing the internal electrode 5 for electrostatic suction outside of the open-to-atmosphere groove 9 and the pocket 11, the arrangement is made at a portion where the pressure of the floating gas is sufficiently low.

The internal electrode 5 may be built in the guide as shown, may be built in the moving body, or may be built in both the guide and the moving body.

With the above configuration, air at a pressure of 5 kgf / cm ² is supplied to the static pressure pad portion 7 while evacuating the pocket 11 with a pump. Most of the air supplied to the static pressure pad portion 7 is exhausted from the chamber through the air release groove 9 through the air release hole 10 to the outside of the chamber. It flows into the pocket 11 and is evacuated from here through the exhaust hole 12 by the pump. As a result, when the bearing gap 6 is 5 μm, the bearing gap 6
The flow rate of the gas finally flowing out of the vacuum chamber is
It is about 10 ⁻⁶ Pam ³ / sec.

In the above state, a repulsive force due to air pressure and an attractive force due to gravity acting on the movable body 1 are acting between the movable body 1 and the guide 2, and in this case, the repulsive force is much more than the attractive force. It is large and it is difficult to maintain a predetermined bearing clearance (5 μm). When a voltage is applied here, an electrostatic attraction force acts between the internal electrode 5 and the metal plate 13, so that the attractive force acting between the moving body 1 and the guide 2 increases, and a predetermined bearing gap (5 μm) is formed. It is possible to hold.

In the static pressure gas bearing having the above-described structure, the space between the internal electrode 5 and the metal plate 13, that is, the gas pressure between the electrode gaps is sufficiently low, so that discharge according to Paschen's law can be prevented. . However, this alone does not provide sufficient measures against discharge. This is because the size of the gap between the electrodes is the same as the floating gap of the air pad, and the electric field generated between the gaps between the electrodes is very large. Therefore, the insulation between the gaps between the electrodes is maintained by a phenomenon called field emission. And discharge may occur.

In this embodiment, in order to prevent this field emission, the gap between the electrodes is formed to be larger than the floating gap of the air pad portion as shown in FIG. With this structure, the electric field generated between the electrode gaps is reduced, and the generation of field emission is suppressed.

[0019]

According to the present invention, since the voltage is applied in a space between the bearings where there is a danger of discharge, it is possible to prevent the operation from being stopped due to the discharge.

[Brief description of the drawings]

FIG. 1 is a sectional view of a hydrostatic gas bearing for vacuum according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a dotted line portion of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Moving body 2 ... Guide 3 ... Electrode terminal 4 ... Internal electric wire 5 ... Internal electrode 6 ... Bearing gap 7 ... Static pressure bad 8 ... Airway 9 ... Atmospheric opening groove 11 ... Pocket 12 ... Exhaust hole 13 ... Metal plate 14 ... Electric wire 15 ... Gap between electrodes

Claims (6)

[Claims] 1. A guide having a guide surface and a moving body moving on the guide surface, wherein the guide or the moving body includes a static pressure pad portion, an atmosphere opening groove portion, and a labyrinth portion, and the labyrinth portion is a fluid. A static pressure gas bearing which can be used in a vacuum by forming an exhaust mechanism, characterized in that it has electrostatic suction means for mutually sucking the moving body and the guide. 2. The static pressure gas bearing according to claim 1, wherein said electrostatic suction means is arranged so as to avoid said static pressure pad portion and said air opening groove portion. 3. The static pressure gas bearing according to claim 1, wherein said electrostatic suction means is arranged so as to avoid said static pressure pad portion, said air opening groove portion and said labyrinth portion. 4. The hydrostatic gas bearing according to claim 1, wherein said electrostatic suction means is formed integrally with said moving body. 5. The hydrostatic gas bearing according to claim 1, wherein said electrostatic suction means is formed integrally with said guide. 6. A dimension between an electrode gap formed between the electrostatic suction means provided on the moving body and the electrostatic suction means provided on the guide is equal to a floating gap of the air pad portion. The hydrostatic gas bearing according to any one of claims 1 to 5, wherein the hydrostatic gas bearing is designed to have a different size.