JP2003065334A - Hydraulic gas bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic gas bearing at a low price which is simply constructed, compact, easy to manufacture, and free from the trouble that the slippage of housing an porous material in an axial direction and the sticking even if an accident happens in the supply of the pressured air. SOLUTION: A shaft body 2 is arranged in the inner periphery of porous material 24 which is fitted in the overall inner peripheral surface of the housing 1, and the inside inner peripheral groove 30 is arranged in at least either of the inner surface of the porous material 24 or the outer periphery of the axial body 2, and the outer part of the housing 1 and the inner part of the axial body 2 are connected by a connecting hole 9 and a vent hole 31 through the groove 30. Also, the outside of the inside inner peripheral groove 33 is equipped respectively on both sides of the inside inner peripheral groove 30 for at least either of the inner peripheral surface of the porous material 24 or the outer peripheral surface of the axial body 30, and the groove 33 is connected with the outside of the housing 1 through the vent hole 35 which is equipped with in the housing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a hydrostatic gas bearing suitable for use as a main shaft of a precision machine, an ultra-precision machine, a shaft supporting a rotary table, or the like.

[0002]

2. Description of the Related Art Conventionally, a rotary joint is attached to one end of a hollow spindle shaft of a static pressure gas bearing, a vacuum adsorption mechanism is arranged at the other end, and a vacuum pump pipe is connected through the rotary joint. A static pressure gas bearing with a vacuum suction mechanism is known. However, this static pressure gas bearing with a vacuum suction mechanism has a rotary joint connected to the shaft end of the spindle shaft opposite to the vacuum suction side. There is a problem that a large torque is required because the frictional resistance of the seal of the joint is added, the cost is increased by the cost of the parts of the rotary joint, and parts other than the rotary joint cannot be attached to the shaft end of the spindle. It was

On the other hand, the applicant of the present invention has previously applied for a static pressure gas bearing with a vacuum adsorption mechanism that solves the above problems (Japanese Patent Laid-Open No. 62-218889). This one is
Instead of a rotary joint attached to the spindle shaft end,
The static pressure gas bearing housing and the hollow shaft are provided with a mechanism equivalent to a rotary joint. FIG. 2 is a sectional view showing the main part of the bearing, in which a hollow cylindrical shaft body 2 is rotatably supported in a fixed housing 1 in a non-contact manner. A pair of ring-shaped porous bodies 4 are attached with an intermediate portion 3 therebetween, the inner peripheral surface of which forms a radial bearing surface 5, which is one bearing surface, and one end surface of which forms a thrust bearing surface 6. Is forming. The shaft body 2 has an opening for vacuum suction (vacuum chuck) of the work W at one end, and an outer peripheral surface of the shaft body 2 forms a radial bearing surface 7 which is the other bearing surface, and a radial clearance 5 is formed on the radial bearing surface 5 through a bearing clearance 8. Facing each other.

Further, a hollow hole H provided in the shaft body 2 is provided, and a communication hole 9 is provided at an intermediate portion in the longitudinal direction of the hollow hole H and opens to the outer peripheral surface of the shaft body. On the other hand, in the intermediate portion 3 of the housing 1, an inner peripheral groove 10 which is continuous in the circumferential direction is provided on the inner peripheral surface so as to face the communicating hole 9, and a vent hole 11 which penetrates from the inner peripheral groove 10 to the outer surface of the housing. Is provided. Then, when a vacuum pipe is connected to the ventilation hole 11 and suction is performed, the ventilation path constituted by the communication hole 9, the inner circumferential groove 10 and the ventilation hole 11 functions as a rotary joint, and the rotating shaft body 2 is exhausted. The work W at the shaft end is attracted to the end surface of the shaft body 2.

The shaft body 2 is supported by the housing 1 through the bearing gap 8 in a non-contact manner by ejecting the pressure gas supplied from the air supply hole 12 from the radial bearing surface 5 of the porous body 4 into the bearing gap 8. . Then, for example, a disk-shaped rotor (not shown) attached to the shaft end and a disk-shaped stator (not shown) attached to the side wall of the housing 1 facing the rotor are rotationally driven.

[0006]

However, in the above-mentioned conventional hydrostatic gas bearing, the porous bodies 4 are axially machined at the inner diameter sides of both ends of the housing 1 and mounted in a pair in the axial direction. Therefore, the following various problems have occurred. If the bearing area is increased with the same diameter to improve load bearing performance, the overall length of the device becomes long and the entire device becomes large. Further, the attachment structure of the porous body 4 is complicated and the manufacturing cost becomes high.

Since the inner end surface of the porous body 4 faces the stepped surface of the intermediate portion 3 of the housing, when the pressurized gas is supplied from the air supply hole 12, the housing 1 and the porous body 4 are axially moved. There is a risk of relative movement and displacement. If an accident such as the supply of pressurized gas is stopped during rotation, the inner diameter surface of the intermediate portion 3 of the housing 1 and the outer diameter surface of the shaft body 2 do not go through the porous body 4. There is a risk of direct contact and burning due to frictional heat.

Therefore, the present invention simplifies the structure by continuously forming the porous body on the inner surface of the housing in the axial direction, is small in size, and is easy to manufacture, and the housing and the porous member are displaced from each other in the axial direction. It is an object of the present invention to provide a static pressure gas bearing that does not have a fear and that does not burn even if there is an accident in the supply of pressurized gas at a low cost.

[0009]

According to a first aspect of the present invention, a shaft body is arranged on the inner periphery of a porous body attached to the inner peripheral surface of a housing, and the hollow hole provided in the shaft body is a communication hole. In the hydrostatic gas bearing that opens to the outer peripheral surface of the shaft body and ejects pressurized gas from the porous body to the shaft body, the porous body covers the entire inner peripheral surface of the housing in the housing. And an inner inner circumferential groove is provided at a position facing the communicating hole on at least one of the inner circumferential surface of the porous body and the outer circumferential surface of the shaft body. Is opened to the outer surface of the housing through a vent hole provided in the porous body and an exhaust hole provided in the housing, and at least one of the inner peripheral surface of the porous body and the outer peripheral surface of the shaft body is an inner surface. Outer inner circumferential grooves are provided on both sides of the inner circumferential groove, and the outer inner circumferential grooves are provided on the porous body. It has a configuration which is open to the outer surface of the housing through an exhaust hole provided in the hole and the housing.

The invention of claim 2 is characterized in that the porous body is formed of graphite. Further, claim 3
The invention of (1) is characterized in that the porous body is continuously and integrally attached to the inner peripheral surface of the housing.

[0011]

The porous body of the present invention is continuous so as to cover the entire inner peripheral surface of the housing and is not axially divided. Therefore, the structure of the bearing is simple and easy to manufacture. In addition, the axial length of the porous body is shorter than that of the conventional product having the same radial bearing area, and the size is reduced.

Further, since the porous body does not have a surface facing the housing in the axial direction, the pressurized gas ejected from the porous body exerts a relative axial pressure between the housing and the porous body. Does not work. Further, since the entire inner peripheral surface of the housing is made of a porous member, if a porous member having good slidability is used, it will not be burned even if the porous body and the shaft come into contact with each other during rotation. .

The static pressure gas bearing of the present invention functions as a vacuum chuck when the inside of the hollow hole provided in the shaft body is evacuated through the communication hole, the inner peripheral groove, and the ventilation hole. On the other hand, when the pressurized gas is sent into the hollow hole provided in the shaft body through the communication hole, the inner peripheral groove inside, and the ventilation hole, it functions as a pressure chuck.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view of an embodiment of the static pressure gas bearing of the present invention. The same or corresponding parts as in the conventional case are designated by the same reference numerals. First, the structure will be described. A shaft 2 is rotatably supported inside a fixed housing 1. Flange-shaped collar portions 2a are attached to both shaft ends of the cylindrical portion of the rotating body 2, one of the collar portions 2a is blind, and the other collar portion 2a has an opening 3a. Although not shown, at least one of the collar portions 2a is detachably screwed in consideration of the assembling of the rotating body 2 to the housing 1.

On the inner peripheral surface of the housing 1, one long cylindrical porous body 24 is fixedly attached to the entire surface. Further, the housing 1 is provided with an air supply passage 26 extending from the screwed air supply hole 12 opening on the outer peripheral surface to the circumferential grooves 25, 25 provided on the outer peripheral surface near the axial end of the porous body 24. The structure is such that pressurized gas is sent to the porous body 24. The inner peripheral surface of the porous body 24 is a radial bearing surface 5 as one bearing surface, and faces the radial bearing surface 7 which is the other bearing surface of the outer peripheral surface of the shaft body 2 through the radial bearing clearance 8. ing. Further, both axial end surfaces of the porous body 24 are thrust bearing surfaces 6 and are opposed to the thrust receiving surfaces 27, which are the inner side surfaces of the flange portions 2 a of the shaft body 2, through the thrust bearing clearances 28.

Communication holes 9 are formed at two intermediate positions in the lengthwise direction of the shaft body 2 so as to penetrate through the wall in the radial direction at a phase of 180 degrees. Two or more communication holes 9 may be provided,
It is preferable to provide them at equally circumferential positions. An inner circumferential groove 30 continuous in the circumferential direction is provided at the intermediate position in the lengthwise direction of the inner circumferential surface of the porous body 24 so as to face the communication hole 9 of the shaft body 2. Further, there is provided a ventilation hole 31 in the radial direction which penetrates the porous body 24 and each side wall of the housing 1 from the inner peripheral groove 30 inside thereof and is opened to the outside. The communicating hole 9, the inner peripheral groove 30 inside, The ventilation hole 31 constitutes a ventilation path of the rotary joint. Further, grooves which are continuous in the circumferential direction with annular inner peripheral land portions 32, 32 are formed as outer inner peripheral grooves 33, 33 at two positions on both sides of the inner inner peripheral groove 30. There is. Then, the inner circumferential grooves 33, 33 on the respective outer sides thereof
A radial exhaust hole 35 that penetrates through the porous body 24 and each side wall of the housing 1 and opens to the outside is provided.

The above-mentioned inner peripheral land portions 32, 32 form a minute gap with the radial receiving surface 7 to form the inner peripheral groove 30.
This is for ensuring a pressure difference between the inner inner circumferential groove 33 and the outer inner circumferential groove 33, and the size of the minute gap corresponds to the magnitude of the pressure in the inner inner circumferential groove 30 (in the case of depressurization and pressurization). (It is considerably different from the case of)). Next, the operation will be described.

When the pressurized gas is supplied from the air supply hole 12 of the housing 1, the pressurized gas reaches the grooves 25, 25 on the outer periphery of the porous body 24 through the air supply passage 26, and from there, the porous body 2 is reached.
4 is supplied to the inner peripheral surface of the radial bearing surface 5 and the outer surface of the thrust bearing surface 6 and is uniformly ejected. As a result, a gas layer having a high pressure is formed in the radial bearing clearance 8 and the thrust bearing clearance 28, and the shaft body 2 is levitationally supported by the housing 1 in a non-contact manner. The ejected pressure gas is discharged into the atmosphere from the outer peripheral grooves 33, 33 through the exhaust hole 35. Further, a part of the ejected pressure gas is also released into the atmosphere from the thrust bearing clearance 28.

In this case, since the porous body 24 is formed on the entire inner peripheral surface of the housing 1 and does not have a surface facing the housing 1 in the axial direction as in the conventional example, the pressure from the porous body 24 is applied. The housing 1 and the porous body 2 by the ejection of gas
The phenomenon that 4 and 4 move relative to each other in the axial direction and are displaced does not occur at all. Also, due to some accident, the air supply hole 1 of the housing
When the supply of the pressurized gas to 2 is stopped, the pressure in the bearing gap 28 decreases and the rotating shaft body 2 sinks in the non-contact state with the porous body 24 until then, and the radial bearing surface 5 and hollow of the porous body are hollowed. The radial receiving surface 7 of the shaft contacts and rotates.
Even in that case, the inner surface of the metal housing 1 does not directly contact the metal radial receiving surface 7, and the porous body 2
4 is in contact with the radial receiving surface 7, the porous body 24
If the material is formed using a material having good slidability such as graphite, seizure of the radial bearing surface 5 can be prevented.

When the static pressure gas bearing functions as a vacuum chuck, a vacuum pipe is connected to the vent hole 31 to suck the gas. As a result, the air in the rotating shaft body communicates with the communication holes 9,
The inside of the hollow hole H of the shaft body is decompressed by being sucked through the inner peripheral groove 30 and the ventilation hole 31, and the work W is vacuum-adsorbed and held by the end surface of the shaft body 2 on the side of the opening 3a. At the time of this vacuum suction, both sides of the inner inner circumferential groove 30 are the outer inner circumferential groove 33 which is open to the atmosphere, but since the gap between the inner circumferential land portion 32 and the radial receiving surface 7 is very small, its exhaust The inside of the inner peripheral groove 30 is maintained at a predetermined reduced pressure by resistance.

On the contrary, when the static pressure gas bearing functions as a pressure chuck, a spring-loaded piston for the pressure chuck is mounted in the hollow hole H of the shaft body 2. When the piston is not pressed, it is pushed by the spring and is in the forward position, and the workpiece W, which is the member to be chucked, is open. At the time of chucking, a pipe of a compressor is connected to the ventilation hole 31 to send pressurized gas into the shaft body 2. The pressurized gas reaches the hollow hole H through the ventilation hole 31, the inner peripheral groove 30, and the communication hole 9 even when the shaft 2 is rotating, pressurizes the spring-loaded piston for the pressure chuck, and resists the pressure of the spring. To retreat. As a result, the work W is held on the end surface of the shaft body 2 on the side of the opening 3a.

Even in the case of this pressurization, the minute gap between the inner peripheral land portion 32 and the radial receiving surface 7 is the outer inner peripheral groove 33.
The pressure difference between the inner peripheral groove 30 and the inner peripheral groove 30 is prevented from decreasing. Incidentally, the three inner circumferential grooves 30, 3 of the porous body 24
3, 33, the pipe connection port of the ventilation hole 31 and the inner peripheral land portion 3
It is preferable to impregnate 2 with a resin to make it difficult for gas to communicate. However, for example, a vacuum pump for exhausting has a sufficient exhaust capacity, and a compressor for pressurizing has a sufficient gas compressing capacity, so there is no practical problem even if these resin impregnations are not performed. .

In the above embodiment, the inner circumferential grooves 30, 33, 33 which are continuous in the circumferential direction are formed at three positions on the inner circumferential surface of the porous body 24, but the present invention is not limited to this. The inner peripheral grooves 30, 33, 33 may be provided on the outer peripheral surface of the shaft body 2,
Alternatively, it may be provided separately on both the inner peripheral surface of the porous body 24 and the outer peripheral surface of the shaft body 2. Further, the circumferentially continuous grooves 30, 33, 33 may be provided at three or more locations depending on the axial length of the porous member 24 (axial length of the housing 1). In that case, if the locations of the grooves are odd, the number of the inner peripheral grooves 30 on the inside is one or an odd number, and at least one vent hole 31 is provided in this groove, and the exhaust holes 35 are provided on the outer peripheral grooves 33, respectively. It may be provided. on the other hand,
If the locations of the grooves are even, the number of inner circumferential grooves 30 is two or even, and at least one vent hole 31 is provided in this groove.
And the exhaust holes 3 are provided in the inner circumferential grooves 33 on the outer side.
5 may be provided.

[0024]

As described above, according to the present invention,
Since one bearing surface of the hydrostatic gas bearing is formed of a porous body that continuously covers the entire inner surface of the housing, the structure is downsized.
This simplifies and facilitates production, and as a result, an effect that it can be produced at low cost is obtained.

Further, since the porous body does not have a surface that faces the housing in the axial direction, the effect that the housing and the porous body do not move and deform relative to each other due to the force of the pressure gas. . Further, since the inner peripheral surface of the housing is covered with the porous body, even if the supply of the pressurized gas is stopped during the rotation of the shaft, the outer peripheral surface of the shaft does not come into contact with the inner peripheral surface of the housing. Therefore, it is possible to obtain an effect that it is possible to prevent the shaft body from being seized on the housing due to frictional heat.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a main part of a conventional static pressure gas bearing.

[Explanation of symbols]

1 housing Biaxial body 9 communication holes 24 Porous body 30 Inner peripheral groove 31 Vents (on housing) 33 Outer circumferential groove 35 Exhaust hole

Claims (3)

[Claims] 1. A shaft body is arranged on the inner circumference of a porous body attached to the inner circumference surface of a housing, and a hollow hole provided in the shaft body opens to the outer circumference surface of the shaft body through a communication hole. In a static pressure gas bearing for ejecting a pressurized gas from the porous body to a shaft body, the porous body is continuously provided in the housing so as to cover the entire inner peripheral surface of the housing. At least one of the inner peripheral surface of the shaft and the outer peripheral surface of the shaft body is provided with an inner inner peripheral groove at a position facing the communication hole, and the inner inner peripheral groove is a ventilation hole and a housing provided in the porous body. Through the exhaust hole provided on the outer surface of the housing, and at least one of the inner peripheral surface of the porous body and the outer peripheral surface of the shaft body has an outer inner peripheral groove on both sides of an inner inner peripheral groove. Are provided respectively, and the inner circumferential groove on the outside is provided with a ventilation hole provided in the porous body and an exhaust gas provided in the housing. Externally pressurized gas bearing, characterized in that the opening in the outer surface of the housing via a. 2. The static pressure gas bearing according to claim 1, wherein the porous body is formed of graphite. 3. The hydrostatic gas bearing according to claim 1, wherein the porous body is continuously and integrally attached to the inner peripheral surface of the housing.