JPH07317768A - Static pressure porous bearing - Google Patents

Abstract

PURPOSE:To provide a static porous bearing which improves bearing rigidity and loading capacity and is capable of restricting self-excited vibration at a low cost. CONSTITUTION:A bearing face a radial bearing face 33, thrust bearing face 35) which is provided in the porous member 30 attached to a housing, which is one of bearing members, is opposed to the other bearing face a radial bearing face 22, thrust bearing face 23) which is provided in the rotary member 20, which is the other bearing member, through a radial bearing clearance 34 or thrust bearing clearance 36, and air is injected from the porous member 30 to the bearing clearances 34 and 36. A groove is provided in at least either the bearing faces 33 and 35 or the other bearing faces 22 and 23.

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 porous bearing used for a spindle, a rotary table, etc. of an ultra-precision machine or a machine tool having a high peripheral speed, and particularly, to improve rigidity, load capacity, The present invention relates to a hydrostatic porous bearing having improved performance such as suppression of self-excited vibration.

[0002]

2. Description of the Related Art As a conventional static pressure type porous bearing of this type, for example, the applicant of the present application previously filed No. 1-7562.
No. 4 (hereinafter referred to as the first conventional example), Japanese Patent Laid-Open No. 4-2666
No. 15 (referred to as a second conventional example) and the like are proposed. In each of these, a cylindrical rotating member, which is the other bearing member, is rotatably supported in a non-contact manner inside a fixed housing, which is one bearing member, with flanged flanges at both ends. ing. A short cylindrical porous member is fixed to the inner peripheral surface of the housing, a radial bearing surface is provided on the inner peripheral surface of the porous member as one bearing surface, and a thrust member is attached to the end surface of the porous member. A bearing surface is provided.

On the other hand, the rotary member is provided with a radial receiving surface on the cylindrical outer peripheral surface as the other bearing surface facing the radial bearing surface via the radial bearing clearance, and also has a flange-shaped flange portion. A thrust receiving surface is provided on the inner end surface as the other bearing surface facing the thrust bearing surface with a thrust bearing clearance therebetween. The thrust receiving surface is provided with a pocket having a depth substantially equal to the bearing clearance continuously in the circumferential direction (first conventional example) or intermittently in the circumferential direction (second conventional example). ing. The pocket functions as a pressure reservoir for compressed air ejected from the porous member into the bearing clearance to improve the bearing performance such as rigidity and load capacity.

[0004]

However, in each of the above-mentioned conventional static pressure porous bearings, there is a pocket that serves as a pressure reservoir for compressed air, which results in self-excited vibration caused by the compressibility of gas. Has a problem that is likely to occur. Therefore, the present invention has been made by paying attention to the above-mentioned conventional problems, and it is difficult to put into practical use the conventional hydrostatic porous bearing which is capable of suppressing bearing vibration while improving bearing rigidity and load capacity. Is intended to be provided at low cost.

[0005]

According to the present invention, which achieves the above object, one bearing surface provided on a porous member attached to one bearing member and another bearing surface provided on the other bearing member are provided. In a static pressure porous bearing which faces through a clearance and ejects gas from a porous member into a bearing clearance, a groove is provided on at least one of one bearing surface and the other bearing surface. is there.

[0006]

[Function] Self-excited vibration occurs when the mass flow rate supplied to the bearing clearance (inflow mass flow rate), the mass flow rate in the bearing clearance, and the mass flow rate released from the bearing clearance to the atmosphere (outflow mass flow rate) are all equal. Does not occur. Therefore, from the standpoint of suppressing self-excited vibration, it is desirable that even when the respective mass flow rates change from the equilibrium state due to changes in the bearing clearance due to external force or the like, the respective changes are reduced.

Incidentally, the depth of the pocket in the hydrostatic porous bearing of the conventional example is about the same as the bearing clearance (the radial bearing clearance is 7 to 13 μm on one side in the diametrical direction, and the thrust bearing clearance is often 5 to 10 μm). Shallow and width 5
It is as wide as -10 mm. On the other hand, in the present invention,
A groove that is deeper and narrower than the pocket functions as a pressure reservoir. Therefore, even if the mass flow rate changes in the bearing due to an external force or the like, each change in the inflow mass flow rate and the outflow mass flow rate can be suppressed to be small.

That is, the inflow mass flow rate is inversely proportional to the pressure in the bearing clearance. Therefore, in the case of the conventional shallow and wide pocket, the change in pressure is large, and therefore the change in the inflow mass flow rate is also large (the inflow mass flow rate remarkably decreases as the pressure in the bearing clearance increases). In the deep and narrow groove of the present invention, the change in the inflow mass flow rate is small because the change in pressure is smaller than that in the conventional pocket.
Moreover, in the case of a relatively deep groove, the pressure hardly changes instantaneously, so there is almost no change in the inflow mass flow rate in the groove portion, and as a result, the change in the inflow mass flow rate becomes smaller overall.

This means that, even when compared with a bearing having no pockets or grooves in the bearing clearance (Comparative Product 3 described later), the flow rate flowing into the groove portion of the present invention is equal to the pressure in the bearing clearance. It is advantageous in offsetting the inflow decrease change amount due to the increase of the flow rate and consequently reducing the total inflow change amount. On the other hand, regarding the outflow mass flow rate, in the case of the conventional pocket, if the bearing clearance becomes narrower due to external force etc. and the pressure inside the bearing clearance increases, the outflow mass flow rate increases because the differential pressure from the atmospheric pressure increases. Become. Further, since the pocket is large (wide), even if the bearing clearance is narrow, the flow resistance in the bearing clearance is small, and therefore the change in the mass flow rate of outflow is large. Therefore, in the deep and narrow groove of the present invention, when the bearing clearance becomes narrow and the pressure in the bearing clearance becomes high, the outflow mass flow rate tries to increase, though not so much as in the case of the conventional pocket. On the other hand, when the bearing clearance becomes narrower, the flow resistance in the bearing clearance increases, so the increase in flow rate due to the increase in pressure is offset by the increase in flow resistance in the bearing clearance, resulting in a smaller change in the outflow mass flow rate. . Further, this is because the groove width of the present invention is narrower than that of a bearing having no pockets or grooves in the bearing clearance (Comparative Product 3 described later).
The flow resistance in the bearing clearance is almost the same as that of a bearing without pockets or grooves, and as a result, the amount of change in the mass flow rate is the same as that of a bearing without pockets or grooves in the bearing clearance. is there. Therefore, in the present invention, the inflow mass flow rate, the mass flow rate in the bearing clearance, and the outflow mass flow rate are more likely to approach an equilibrium state than in the conventional case, and self-excited vibration is suppressed.

Regarding the bearing performance such as bearing rigidity and load capacity, the groove provided in the bearing clearance acts as a pressure reservoir for gas, and the static pressure in the groove becomes higher than the pressure in the bearing clearance. Bearing rigidity and load capacity are greater than those of bearings that do not have pockets or grooves in the bearing clearance.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a bearing structure to which the present invention is applied. The cylindrical or angular housing 10, which is one bearing member, is fixed and supported by a fixing member (not shown). A rotating member 20, which is the other bearing member, is rotatably supported inside the housing 10 with the center axis of rotation as X. Flange-shaped flange portions 21 and 21 are fixedly provided on both axial ends of the cylindrical portion of the rotating member 20. At least one of the collar portions 21 is detachably screwed in consideration of the assembling of the rotary member 20 to the housing 10.

Two short cylindrical porous members 30, 30 are fixed to the inner peripheral surface of the housing 10 at some intervals in the axial direction. Further, the housing 10 is provided with air supply holes 11 and 11 and an annular air supply chamber 1 following the air supply holes 11 and 11 for sending compressed air from the outer peripheral surface to the porous members 30 and 30.
2 and 12 are provided respectively, and an exhaust hole 13 that is located between the left and right porous members 30 and 30 and extends from the inner surface of the housing to the outer surface thereof is provided.

The porous member 30 of this embodiment is made of a graphite material having pores, has a core portion 31 having a selected air permeability, and the outer peripheral surface layer of the core portion 31 is impregnated with, for example, phenol resin. The surface stop layer 32 is formed by reducing material holes by clogging. The inner peripheral surface of the porous member 30 constitutes a radial bearing surface 33 which is one bearing surface, and the radial bearing clearance 34
(7 to 13 μm on one side in the diameter direction) is opposed to the radial bearing surface 22 on the outer peripheral surface of the rotary member 20 which is the other bearing surface.

The annular outer end surface of each porous member 30 constitutes a thrust bearing surface 35 which is one bearing surface. On the other hand, the inner surface of each flange 21 of the rotary member 20 is a thrust bearing surface 23 which is the other bearing surface, and faces the thrust bearing surface 35 with a thrust bearing clearance 36. FIG. 2A shows a first embodiment in which the present invention is applied to the thrust bearing portion of the bearing shown in FIG.
(B) shows the details of the groove.

An annular thrust receiving surface 23 provided on the inner side surface of the collar portion 21 of the rotary member as the other bearing surface.
In addition, a thin (narrow) groove 40 having a V-shaped cross section is formed in an annular shape near the outer circumference. Groove 4 of this embodiment
The depth 0 is 70 μm (0.07 mm), which is 7 to 14 times the interval 5 to 10 μm between the thrust bearing clearances 36. Groove width is about 250 μm (0.25 mm), groove diameter is 89
mm.

Two short cylindrical porous members 30, 30 are fixed to the inner peripheral surface of the housing 10 at a slight interval in the axial direction. Also, the housing 10
Although not shown, each porous member 3 is
An air supply hole and an annular air supply chamber subsequent to the air supply hole are provided to feed compressed air into the housings 0 and 30, respectively, and the housing 10 is located between the left and right porous members 30 and 30.
Exhaust holes are provided from the inner surface to the outer surface.

Next, the operation will be described. When compressed air is supplied from the air supply hole 11 of the housing 10, the compressed air enters the porous member 30 through the air supply chamber 12, and passes therethrough to the radial bearing surface 33 and the outer end surface of the inner peripheral surface of the porous member. From the thrust bearing surface 35. This allows
An air layer having a high pressure is formed in the radial bearing clearance 34 and the thrust bearing clearance 36, and the rotating member 20 is supported by the housing 10 so as to float in a non-contact manner. Radial bearing surface 3
The compressed air ejected from 3 continuously forms an air film in the radial bearing clearance 34 to support the rotary member 20 in the radial direction and continuously flows from the exhaust hole 13 into the atmosphere. Also,
The compressed air jetted from the thrust bearing surface 35 forms an air film in the thrust bearing clearance 36 to support the rotary member 20 in the thrust direction and is discharged as indicated by arrow A.

However, in supporting the rotating member 20 in the radial direction and the thrust direction by thus generating the static pressure by the air jet, the groove 40 on the thrust receiving surface 23 is smaller than the gap of the thrust bearing clearance 36. Depth 1
Thrust bearing clearance 36
Since a constant high air pressure is formed over the entire circumference, the thrust load capacity and rigidity of the hydrostatic porous bearing can be increased.

Regarding the self-excited vibration, the groove 40 is also used.
Since the groove width of is as small as about 0.25 mm, the thrust bearing clearance 36
There is almost no effect on the resistance of the gas flowing therein, and therefore the amount of change in the mass flow rate of the outflow can be small (equivalent to a bearing having no pockets in the bearing clearance), and the depth of the groove 40 is the thrust bearing clearance 36. Since it is about 10 times as deep as the distance of, the instantaneous pressure change is small, so there is almost no change in the mass flow rate flowing into the groove portion (advantageous compared to a bearing having no pockets in the bearing clearance). Eventually, the amount of change in the mass flow rate of the inflow can be reduced, so that self-excited vibration is suppressed.

FIG. 3 shows another embodiment. This example
Two circular grooves 4 are formed on the thrust receiving surface 23 of the rotating member 20.
1 and 42 is different from the first embodiment. The depth of the outer groove 41 is 50 μm (0.05 mm), the groove width is about 173 μm (0.17 mm), and the groove diameter is 89 mm.
Is. The inner groove 42 has a depth of 35 μm (0.035 mm)
The groove width is about 100 μm (0.10 mm) and the groove diameter is 62.
mm.

In this embodiment, the depths of the grooves 41 and 42 are set so that the volume of the groove 40 of the first embodiment and the total groove volume of the two grooves 41 and 42 are approximately the same. Has been set. The operation and effect are similar to those of the first embodiment. FIG. 4 shows still another embodiment. This is an application of the present invention to a radial bearing. That is, the radial receiving surface 22 which is the other bearing surface of the rotary member 20 of the hydrostatic porous bearing shown in FIG. 1 is provided with a groove 45 that goes around the circumferential surface. In this embodiment, two grooves 45 are provided for each radial bearing surface 33 of each porous member 30, the groove depth is 40 μm (0.04 mm) and the groove width is about 138 μ.
m (0.14 mm). When the groove is formed in the radial bearing portion, the groove depth is set to the radial bearing in order to prevent the compressed air from wrapping around the eccentricity of the central axis X of the rotating member 20 in the circumferential direction (conduction effect). It is about 5 times the clearance 34.

The operation and effect of this embodiment are substantially the same as those of the first embodiment. Although the groove 45 of the third embodiment is a circumferential groove continuous in the circumferential direction, the present invention is not limited to this, and
It may be formed by intermittently forming grooves in the circumferential direction. FIG. 5 shows the invention product of the present invention, the comparative product 1 having a pocket, the comparative product 2 having a pocket, and the comparative product 3 having no pocket or groove.
For each rotating member of No. 3, three test bodies (No.
1-No. 3. In this experiment, the results of axial rigidity measurement performed using three housings containing porous members of the same specifications) are shown in a graph for comparison. FIG. 6 is a sectional view of a comparative product 1 having a conventional pocket and FIG. 7 is a sectional view of a comparative product 2 having a conventional pocket.

From the results of FIG. 5, regarding the axial rigidity, the comparative product 2 having the wide pocket P has the highest rigidity, and the invention product and the comparative product 1 having the narrower pocket P have substantially the same axial rigidity. It can be said that the comparative product 3, which has rigidity and is next to the comparative product 2 in which neither pocket nor groove is provided, has the lowest axial rigidity. That is, the hydrostatic porous bearing of the present invention has an axial rigidity 10 to 15% higher than that of the hydrostatic porous bearing having neither pockets nor grooves.

FIG. 8 is a graph showing a comparison of the measurement results of the self-excited vibration suppression effect performed on the above four types of static pressure porous bearings. The test was carried out by sequentially mounting a load on the flange-shaped collar portion of each static pressure porous bearing and measuring the supply pressure at which self-excited vibration occurred at that time. (Note that the supply pressure in this test was set to a maximum of 10 kgf / cm ² (G).) From the results in FIG. 8, regarding the supply pressure at which self-excited vibration occurs, in the case of this example, It is clear that regardless of the increase of the loading load, it is stable and does not occur under high supply pressure, and the self-excited vibration suppression effect is great. On the other hand, in all the other cases, self-excited vibration is likely to occur as the mounting load increases. In other words, the payload 7
At 0 kg, self-excited vibration occurs from a supply pressure of about 7 kgf / cm ² (G) in a static pressure porous bearing with no pockets or grooves, and in comparison products 1 and 2 each supply pressure is about 5
It occurred as early as kgf / cm ² (G) and 4.0 kgf / cm ² (G). On the other hand, in the case of the hydrostatic porous bearing of the present invention, the supply pressure is about 9.5 kgf / cm.
The occurrence of self-excited vibration is suppressed up to ² (G).

In each of the above embodiments, the case where graphite is used as the porous member has been described, but the present invention is not limited to this, and other porous members,
For example, a carbon or metal porous member or a ceramic porous member may be used. The groove depth is 5 to the bearing clearance.
10 times is preferable for obtaining the effect of the present invention. However, even if it deviates from this range, it is still included in the scope of the present invention.
And the effect of this invention is acquired.

The groove width is preferably 1 mm or less in order to obtain the effects of the present invention. However, even if it deviates from this range, it is included in the scope of the present invention, and the effects of the present invention can be obtained. Further, the groove may be provided only on one bearing surface, may be provided only on the other bearing surface, or may be provided on both one bearing surface and the other bearing surface.

In addition, although the radial bearing and the thrust bearing are communicated and provided side by side in the above-described embodiments, the present invention is also applicable to the radial bearing alone or the thrust bearing alone. Further, in the above-described embodiment, the case where the present invention is applied to the rotary static pressure porous bearing has been described, but the present invention is not limited to this and can be applied to a direct-acting static pressure porous bearing.

As for the shape of the groove, a V-shaped groove having a low processing cost is shown, but a groove pattern of any other shape having a width of 1 mm or less can be used.

[0029]

As described above, according to the hydrostatic porous bearing of the present invention, since the groove is provided on at least one of the one bearing surface and the other bearing surface, the pressure of the supply gas is locally applied. It is possible to improve the bearing performance such as static rigidity and load capacity at the same time, and at the same time, it is possible to reduce the variation of the inflow mass flow rate and the outflow mass flow rate into the bearing clearance, and as a result, it is possible to suppress self-excited vibration. Has the effect.

If the groove shape is V-shaped, it is easy to manufacture and can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a sectional view of a bearing structure to which the present invention is applied.

FIG. 2A is a detailed cross-sectional view of a main part of the first embodiment of the present invention, and FIG. 2B is an enlarged view of part B of FIG.

FIG. 3 is a detailed cross-sectional view of the essential parts of another embodiment of the present invention.

FIG. 4 is a detailed cross-sectional view of a main part of still another embodiment of the present invention.

FIG. 5 is a graph illustrating the effect of improving the axial rigidity of the invention product.

FIG. 6 is a detailed cross-sectional view of a main part of a hydrostatic porous bearing of a conventional example (Comparative Product 1).

FIG. 7 is a detailed cross-sectional view of a main part of a hydrostatic porous bearing of a conventional example (Comparative Product 2).

FIG. 8 is a graph illustrating the self-excited vibration suppression effect of the invention product.

[Explanation of symbols]

 10 One bearing member (housing) 20 The other bearing member (rotating member) 22 The other bearing surface (radial receiving surface) 23 The other bearing surface (thrust receiving surface) 30 Porous member 33 One bearing surface (radial bearing surface) ) 34 radial bearing clearance 35 one bearing surface (thrust bearing surface) 36 thrust bearing clearance 40 groove 41 groove 42 groove 45 groove

Claims (1)

[Claims] 1. A bearing member provided on a porous member attached to one bearing member faces one bearing surface provided on the other bearing member through a bearing clearance, and a bearing clearance from the porous member. A hydrostatic porous bearing for ejecting gas to a substrate, characterized in that a groove is provided in at least one of the one bearing surface and the other bearing surface.