JPH06173952A - Static pressure fluid bearing - Google Patents

Abstract

PURPOSE:To improve the bearing rigidity and adapt to high-speed rotation by setting both ends of a radial bearing to the opened state to the outside air, and setting only one side of a thrust bearing to the opened state to the outside air. CONSTITUTION:When the pressure gas is guided to an intake hole 5, the pressure gas is squeezed by a cylindrical porous member 2 and a circular porous member 3, flows into a bearing gap Cr between a rotary shaft 1 and a bearing, and rotatably supports the rotary shaft 1 in no contact. The pressure gas of a radial bearing is discharged to the outside from a center discharge hole 6 and a radial bearing end section discharge hole 7, the pressure gas of a thrust bearing on the opposite side to a gas sump 8 is discharged to the outside as it is, the pressure gas on the gas sump 8 side is partially discharged from the radial bearing end section discharge hole 7 because the seal section 2a of the cylindrical porous member 2 has the same gap as the bearing gap Cr and serves as discharge resistance, and the gas sump 8 is kept at the pressure Pm higher than the external pressure Pa. The thrust rigidity can be improved without reducing the radial rigidity, and high bearing rigidity is obtained. This device can be miniaturized, and it can be used at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic bearing used for precision machine tools and measuring machines, and more particularly to a small hydrostatic bearing having high bearing rigidity and suitable for high speed rotation.

[0002]

2. Description of the Related Art Since a hydrostatic bearing has almost no friction, the torque due to rotational friction is extremely small, and due to the fluid averaging effect, a motion accuracy higher by one digit than that of the parts constituting the hydrostatic bearing is realized. Therefore, it has been widely used for precision machine tools, measuring machines and the like, which require particularly high precision movement. Conventionally, in order to improve the rigidity of the hydrostatic bearing, the method described below has been adopted.

(A) To increase the bearing area, the shaft diameter of the bearing is increased. (B) The clearance between the bearing and the rotating shaft is reduced. (C) The pressure of the pressurized fluid supplied is increased.

[0004]

However, the above-mentioned prior art has the following problems.

In the method (a), if the diameter of the hydrostatic bearing is increased, the amount of heat generated by viscous friction of the pressurized fluid increases when the rotating shaft is rotated at a high speed in a machine tool, etc. The amount of thermal expansion of the shaft and bearing increases. Further, since the dimensional change due to the centrifugal force deformation of the rotary shaft becomes large, the rotary shaft and the bearing are likely to come into contact with each other, which impedes high-speed rotation. Further, since the mass of the rotating shaft becomes large, it takes a long time to control the number of rotations, particularly to start and stop the rotating shaft, and it is difficult to achieve high-speed rotation due to the reduction of the resonance frequency.

In the method (b), the amount of heat generated when rotating at high speed is inversely proportional to the bearing clearance, so the problem of thermal deformation becomes more serious. Further, even in the case of a measuring machine that does not rotate at a high speed, if the bearing gap is reduced to about the accuracy of the parts that make up the hydrostatic bearing, there is a problem that the accuracy of rotation is deteriorated because a sufficient fluid averaging effect cannot be obtained. .

In the method (c), generally, there is an upper limit to the pressurized fluid that can be supplied in a factory or the like, and when the pressurized fluid has a high pressure, when a compressed fluid such as gas is used as the working fluid. Has a problem that unstable vibration is likely to occur.

The present invention has been made in view of the problems of the above-mentioned prior art. Particularly, in a small hydrostatic bearing, the hydrostatic bearing has higher bearing rigidity than that of the prior art and is suitable for high speed rotation. An object is to provide a fluid bearing.

[0009]

To achieve the above object, the hydrostatic bearing of the present invention includes a bearing housing including a radial bearing portion and a thrust bearing portion, the radial bearing portion and the thrust bearing portion. The radial bearing is characterized in that both ends are open to the outside air, and only one side of the thrust bearing is open to the outside air. By configuring in this way, especially in a small hydrostatic bearing,
The thrust bearing has a small width and a high bearing rigidity can be obtained even with a hydrostatic bearing in which the pressure in the bearing gap does not rise sufficiently against the supply pressure of the pressurized fluid, and a conventional hydrostatic bearing with the same rigidity can be obtained. On the other hand, since the size can be reduced, the speed can be increased.

[0010]

1 is a schematic sectional view showing a first embodiment of the present invention, showing an example of a porous hydrostatic gas bearing which is one of hydrostatic fluid bearings. In the figure, 1 is a rotating shaft, 2 is a cylindrical porous member forming a radial bearing, 3 is an annular porous member forming a thrust bearing, 4 is a cylindrical porous member 2 and an annular porous member 3. Bearing housing,
5 is a cylindrical porous member 2 provided in the bearing housing 4.
And an air supply hole communicating with the annular porous member 3, 6 is a central exhaust port opened in a cylindrical porous member provided at the axial center of the radial bearing of the bearing housing 2, and 7 is both ends of the radial bearing of the bearing housing 4. Is a radial bearing end exhaust hole provided in the cylindrical porous member 2, and 8 is a gas pool in which high-pressure gas is present.

When the pressurized gas supplied from the well-known pressurized gas supply source is introduced into the air supply hole 5, the pressurized gas is supplied to the cylindrical porous member 2
Also, the rotary shaft 1 is squeezed by the annular porous member 3, flows into a bearing gap formed between the rotary shaft 1 and the rotary shaft 1, and the rotary shaft 1 can be rotatably supported in a non-contact manner by the pressure generated there. After that, the pressurized gas supplied to the radial bearing is fed to the central exhaust hole 6
And, it is exhausted to the outside through the radial bearing end exhaust hole 7.
On the other hand, the pressurized gas supplied to the thrust bearing 8
The other side is discharged to the outside as it is, but since the seal portion 2a of the cylindrical porous member 2 has a clearance equal to the bearing clearance Cr on the gas reservoir 8 side, this becomes exhaust resistance and becomes a radial bearing end. Although part of the gas is exhausted from the partial exhaust hole 7, the gas pool 8 is kept at a pressure Pm higher than the external pressure Pa. A schematic representation of the pressure distribution at this time is shown in the upper part of this figure for the radial bearing and in the right part for the thrust bearing.

Generally, in the pressure distribution of the bearing portion, it is desirable that the maximum value of the pressure distribution be close to Ps with respect to the supply pressure Ps as shown by α in FIG. 2, but when the width Lt of the bearing is small, As a result, the maximum value of the pressure distribution becomes significantly smaller than the supply pressure Ps. At this time,
As a countermeasure, it is effective to increase the transmittance of the porous member or to reduce the bearing gap, but there are cases where the above-mentioned countermeasure cannot be taken due to the problems of unstable vibration and heat generation.
Also, by closing the radial bearing end exhaust hole 7 in FIG. 1, a pressure distribution similar to that of the present invention is obtained for the thrust bearing, but a reduction in radial rigidity cannot be avoided. In such a case, the radial bearing according to the present invention has both ends open to the outside air, and only one side of the thrust bearing is opened to the outside air to realize the pressure distribution shown in γ in the figure. This makes it possible to improve the thrust rigidity without reducing the radial rigidity.

According to the fluid analysis of the bearing clearance, for example, the radial bearing portion diameter is 70 mm, the bearing width is 35 mm, the thrust bearing outer diameter is 98 mm, and the inner diameter is 72 mm.
When the radial bearing end exhaust hole 7 is not opened under the conditions of MPa and bearing gap 5 μm, radial rigidity: 200 N / μm and thrust rigidity: 218 N / μm are obtained. When the radial bearing end exhaust hole 7 is not opened and the gas reservoir 8 is communicated with the outside air, the radial rigidity is 282 N / μm and the thrust rigidity is 147 N / μm. On the other hand, by providing the gas reservoir 8 and opening the radial bearing end exhaust hole to the outside as in the present embodiment, it is possible to achieve the higher rigidity in both radial and thrust of the above two conditions. .

As means for providing an exhaust hole at the end of the radial bearing, a circumferential annular groove is formed in the cylindrical porous member 2 as shown in FIG. 1, and a circle is formed on the rotary shaft 1 side as shown in FIG. Even if the circumferential annular groove is formed, the same effect can be obtained.

FIG. 4 shows a second embodiment of the present invention, which is an embodiment in which the thrust plate 1a of the rotary shaft 1 is arranged in the center. 1 shows an example of a porous hydrostatic gas bearing, which is one of hydrostatic bearings.
In the figure, 1 is a rotating shaft, 2 is a cylindrical porous member forming a radial bearing, 3 is an annular porous member forming a thrust bearing, 4 is a cylindrical porous member 2 and an annular porous member 3. A bearing housing, 5 is an air supply hole communicating with the cylindrical porous member 2 and the annular porous member 3 provided in the bearing housing 4, and 9 is a bearing communicating between the cylindrical porous member 2 and the annular porous member 3. Radial / thrust exhaust holes 10 provided in the housing 4 are thrust bearing exhaust communication portions.

When the pressurized gas supplied from the well-known pressurized gas supply source is introduced into the air supply hole 5, the pressurized gas is supplied to the cylindrical porous member 2.
Also, the rotary shaft 1 is squeezed by the annular porous member 3, flows into a bearing gap formed between the rotary shaft 1 and the rotary shaft 1, and the rotary shaft 1 can be rotatably supported in a non-contact manner by the pressure generated there. Thereafter, the pressurized gas supplied to the radial bearing is exhausted to the outside from the radial-thrust exhaust hole 9 and the axial direction. On the other hand, the pressurized gas supplied to the thrust bearing is exhausted to the outside through the radial / thrust exhaust hole on the inner peripheral side, but the outer peripheral portion has no gas in the thrust bearing exhaust communication section 10 of the two thrust bearings. Since it does not flow, it is maintained at a pressure Pm higher than the outside air Pa. A schematic representation of the pressure distribution at this time is shown in the right part of the thrust bearing. The pressure distribution of the radial bearing is the same as that of the first embodiment of the present invention shown in FIG. Therefore, also in this embodiment, the same effect as that of the first embodiment can be obtained, and it is possible to obtain a static pressure gas bearing having a small size and high rigidity.

[0017]

According to the present invention, particularly in a small-sized hydrostatic bearing, even if the hydrostatic bearing is such that the thrust bearing has a small width and the pressure in the bearing gap does not rise sufficiently with respect to the supply pressure of the pressurized fluid, High bearing rigidity can be obtained, and downsizing can be achieved as compared with the conventional hydrostatic bearing having the same rigidity, so that high speed can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a hydrostatic bearing according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of pressure distribution in a bearing gap.

FIG. 3 is a second example of the radial bearing end exhaust method according to the present invention.

FIG. 4 is a schematic diagram of a hydrostatic bearing according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Rotating Shaft 1a Thrust Plate 2 Annular Porous Member 2a Seal Part 3 Annular Porous Member 4 Bearing Housing 5 Air Supply Hole 6 Central Exhaust Hole 7 Radial Bearing End Exhaust Hole 8 Gas Reservoir 9 Radial / Thrust Exhaust Hole 10 Thrust Bearing Exhaust communication part

Claims (3)

[Claims] 1. A hydrostatic bearing comprising a bearing housing including a radial bearing portion and a thrust bearing portion, and a rotary shaft supported in a non-contact manner by the radial bearing portion and the thrust bearing portion, wherein the radial bearings have opposite ends. Is opened to the outside air, and the thrust bearing has only one side opened to the outside air. 2. Between the radial bearing portion and the thrust bearing portion, only one side of the thrust bearing portion is provided by communicating the outside air with the radial bearing end portion or the circumferential groove provided in the rotary shaft. The hydrostatic bearing according to claim 1, wherein the hydrostatic bearing is released to the outside air. 3. The method according to claim 1, wherein only one side of the thrust bearing portion is released to the outside air by not releasing the exhaust communication portions of the two thrust bearing portions facing the one thrust plate to the outside air. Hydrostatic bearing.