JP4031867B2 - Hydrostatic air bearing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static pressure air bearing device, and more specifically, for example, a static pressure air bearing device used in a precision processing machine or precision inspection machine such as a high-speed spindle device for semiconductor wafer grinding. It is about improvement.
[0002]
[Prior art]
The hydrostatic air bearing has a small bearing gap between the movable part and the fixed part, introduces compressed air into the bearing gap via a pressure adjusting means such as a throttle valve, and the high pressure air introduced into the bearing gap. The movable part is supported in a non-contact state with respect to the fixed part by the pressure of. Hydrostatic air bearings have extremely low frictional resistance when compared with conventional oil lubricated bearings, and because of the so-called averaging effect, guide accuracy higher than the shape accuracy of the bearing surface can be obtained. It is used as a bearing device such as a spindle of a machine or a precision inspection machine or a linear guide device, and its usefulness is evaluated.
[0003]
The pressure adjustment means incorporated in the hydrostatic air bearing includes a self-contained throttle with a fine hole in the bearing surface, an orifice throttle, a slot throttle that uses a flow resistance in a narrow gap, and a porous material communication hole. A porous diaphragm that uses the surface, a shallow diaphragm that communicates with the air supply source on the bearing surface, and a surface diaphragm that changes the flow resistance in the flow direction have been put into practical use.
[0004]
[Problems to be solved by the invention]
Static pressure air bearings use low-viscosity and compressible gas, such as air, as a lubricating medium, so the above advantages are evaluated, but support rigidity compared to oil-lubricated bearings. In addition, it has been pointed out that the damping performance of vibration and vibration is low, and the usable industrial field is restricted. For this reason, in recent years, there has been a strong demand for improvement in support rigidity and vibration damping performance even in hydrostatic air bearings, as a further improvement in accuracy is required for an object to be processed or inspected.
[0005]
In order to meet these demands, a composite throttle combining a self-made throttle or an orifice diaphragm and a shallow groove has been proposed as a means to increase the support rigidity of a hydrostatic air bearing. It has been pointed out that the self-excited vibration occurs when the damping performance of the groove decreases and the volume of the shallow groove exceeds a certain limit. On the other hand, a method of increasing the bearing supply air pressure has been studied. However, when this method is adopted, the support rigidity is proportionally increased, but there is a problem in that it is difficult to avoid a decrease in vibration damping performance. As another method, a method of improving both the support rigidity and the damping coefficient by narrowing the bearing gap has been proposed. However, when the bearing gap is narrowed, the influence of the thermal deformation of the bearing component due to the temperature rise is caused. It becomes large and stable bearing performance cannot be obtained. In addition, when the bearing gap is set to be narrow, it is necessary to strictly manage the dimensional accuracy and shape accuracy of the bearing constituent members, which increases the manufacturing cost of the hydrostatic air bearing.
[0006]
The main object of the present invention is to provide a high-precision hydrostatic air bearing with improved support rigidity and vibration damping performance.
[0007]
[Means for Solving the Problems]
In the present invention, a compressed air storage space (hereinafter referred to as a pressurized space) is provided adjacent to the bearing gap, and the pressure of the compressed air supplied into the pressurized space is higher than the ambient atmospheric pressure. The pressure in the entire bearing gap is increased by this, thereby improving the support rigidity and vibration damping performance of the hydrostatic air bearing device.
Specifically, as described in claim 1, bearing surfaces facing each other are provided on the fixed portion and the movable portion, and compressed air is supplied to the bearing gap formed between the two bearing surfaces via an air supply throttle. Compressed air that is supplied and communicated with the bearing gap on both sides in the axial direction of the bearing gap and introduced into the bearing in the hydrostatic air bearing in which the movable part is held in a non-contact state with respect to the fixed part. A pressure space that can be set to a pressure higher than the ambient atmospheric pressure, and an air supply line that communicates with the pressure space is provided on the fixed portion side, and the air supply line is connected via a pressure adjusting means. It is connected to a compressed air source.
[0008]
The present invention also Zinal aperture, restrictive orifice, the double-sided versus countercurrent type aerostatic thrust bearing with a supply air pressure adjustment means is arranged on the bearing surface such as a porous diaphragm, or the inner circumferential side of one of the thrust plate In a state adjacent to the bearing gap outlet provided on the outer peripheral side, a pressurized space isolated from the outside of the bearing device is interposed between the fixed part and the movable part of the bearing member via the bearing gap and the non-contact seal part. By forming and maintaining the pressure of the compressed air supplied in this pressurized space higher than the ambient atmospheric pressure, the pressure of the entire bearing gap is increased, thereby supporting rigidity and vibration of the hydrostatic air thrust bearing Attenuation performance is improved.
Specifically, as described in claim 2, in the hydrostatic air thrust bearing device including the double-sided opposed thrust plate, adjacent to the bearing clearance outlet provided on the inner peripheral side or the outer peripheral side of the thrust plate. A pressure space isolated from the outside of the bearing device is formed between the fixed portion of the bearing member and the movable portion of the main shaft member via the bearing gap and the non-contact seal portion, and the bearing gap An air supply conduit for introducing compressed air from the compressed air source into the pressurized space is connected to the inlet of the compressor, and a means for adjusting the compressed air pressure flowing into the pressurized space is provided in the air supply conduit. It is characterized by that.
[0009]
A pressure space is provided adjacent to the bearing gap, and the pressure of the compressed air supplied to the pressure space is maintained at a pressure higher than the ambient atmospheric pressure, thereby increasing the pressure of the entire bearing gap, thereby reducing static pressure. Improve support rigidity and vibration damping performance of compressed air bearing device. The present invention can be applied to both a hydrostatic air radial bearing device and a hydrostatic air thrust bearing device to achieve the above-described effects.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 14 attached to the specification.
[0011]
First, FIG. 1 shows a case where the present invention is applied to a radial bearing. As shown in FIG. 1A, the outer diameter surface of the shaft (1) and the inner diameter surface of the bearing portion (2) are minute bearings. A hydrostatic air radial bearing is constructed by supplying compressed air from a compressed air source (not shown) to a plurality of air supply throttles (4) facing each other through the gap (3) and communicating with the bearing surface. ing. Circumferential groove-shaped pressurizing spaces (5) and (5 ') are provided at both ends in the axial direction of the bearing portion (2), and the pressurizing spaces (5) and (5') are non-contact seal portions (6). It is partitioned from the space outside the bearing by (6 '). The seal gap (7) (7 ') in the non-contact portion is a minute gap similar to the bearing gap (3), and the bearing exhaust flowing out from the bearing gap (3) is removed from the seal gap (7) (7'). The internal pressure of the pressurizing space (5) (5 ') is kept higher than the atmospheric pressure outside the shaft.
[0012]
By providing such a pressurized space, as shown by the oblique lines in FIG. 1 (B), the hydrostatic air bearing of the present invention can reduce the pressure of the entire bearing gap as compared with the conventional hydrostatic air bearing. The vibration damping performance is improved. In FIG. 1B, among the broken lines indicating the pressure distribution, the solid line indicates the pressure distribution when the pressurizing space (5) (5 ′) is provided, and the dotted line indicates the pressure distribution when the pressurizing space is not provided. The air flowing out from the seal gap (7) (7 ') is discharged out of the system through the exhaust pipes (9) (9') provided in the housing (8). Therefore, the air pressure at the outlet of the seal gap (7) (7 ′) becomes equal to the atmospheric pressure.
[0013]
If the pressure in the pressurized space (5) (5 ') is not constant along the circumferential direction, unstable vibration may occur. Therefore, the dimensions of the pressurized space (5) (5') are It is necessary to select the flow resistance along the direction so that it can be ignored as compared with the bearing clearance. The supply throttle (4) is illustrated as a self-contained throttle in FIG. 1, but an orifice diaphragm, a porous throttle, a surface throttle, a slot throttle, a supply hole throttle (self-made throttle, Alternatively, other aperture methods such as a composite aperture comprising an orifice aperture) and a shallow groove can be used.
[0014]
In the configuration shown in FIG. 1, if the dimensions of the bearing and the clearance between the non-contact seal portions (6) and (6 ') are determined, the air pressure inside the pressurized space (5) and (5') will be a constant value. Maintained. On the other hand, the static stiffness of the hydrostatic air bearing is maximized when the ratio of the pressure on the supply side of the supply throttle (4) provided on the bearing surface and the bearing gap (3) side takes a certain optimum value. Therefore, 'the Rukoto teapot subjected compressed air via a pressure regulating valve (not shown), the pressurizing space (5) (5 pressurized space (5) (5)' adjusting the air pressure in) By doing so, it becomes possible to bring the pressure ratio of the air supply throttle (4) on the bearing surface close to the optimum value, and a hydrostatic air bearing with high support rigidity can be obtained.
[0015]
It is also possible to adjust the bearing characteristics by adjusting the air pressure in the pressurizing space (5) (5 ′) during use. However, in order to increase the static rigidity of the hydrostatic air bearing by operating the air supply restrictor (4) on the bearing surface normally, when the compressed air is introduced into the pressurized space (5) (5 '), The air pressure in the pressure space (5) (5 ′) needs to be controlled in a range where the pressure at the outlet of the air supply throttle (4) on the bearing surface is lower than the supply pressure to the hydrostatic air bearing. Also, if the internal pressure in the pressurizing space (5) (5 ') changes in response to the change in the bearing clearance (3), the delay in pressure change in the pressurizing space (5) (5') This reduces the damping performance and causes self-excited vibration. If the change of the internal pressure of the pressurized space (5) (5 ') is suppressed by the operation of the pressure adjustment means, for example, the air supply throttle (4), the self-excited vibration is prevented and the vibration damping performance is improved. Can be made. Note that the air supply conduits to the pressurizing spaces (5) and (5 ′) need to have a sufficiently large cross-sectional area so as not to cause a throttling action.
[0016]
FIG. 2 shows a connection of a supply air line (10) connected to a compressed air source via a pressure control valve (11) to the pressurized space (5) (5 ′). Fig. 3 shows a hydrostatic air radial bearing whose internal pressure is adjustable. In this embodiment, a slot throttle that uses a throttle action of a narrow gap (12) extending in a direction orthogonal to the axis of the shaft (1) is provided as the supply throttle.
[0017]
Further, FIG. 3 shows that the exhaust pipe (14) extending outside the hydrostatic air bearing is connected to the pressurizing space (5) (5 ′) via the throttle valve (13). A comparative example is shown in which the internal pressure of the pressurized space (5) (5 ') can be adjusted by restricting the exhaust gas flowing out from 5') toward the outer space of the bearing. As the air supply throttle, a porous throttle using an air-permeable porous material (15) is used.
[0018]
In the embodiment shown in FIG. 1, the pressurizing spaces (5) and (5 ') are provided at both ends along the axial direction of the hydrostatic air bearing. May be obtained. In addition, when providing a pressurized space on one side with a static pressure air bearing that employs a type of throttle that allows compressed air to flow in a limited range of the bearing surface, such as an air supply aperture throttle, a composite aperture, or a slot aperture, Even when the pressure in the bearing gap (3) increases due to the formation of the pressurized space by providing an air supply throttle in the vicinity of the bearing gap outlet on the opposite side of the pressurized space, where the pressure is equal to the ambient atmospheric pressure. The pressure ratio between the supply side and the bearing clearance side of the supply throttle can be brought close to the optimum value.
[0019]
FIG. 4 shows a composite throttle comprising an air supply throttle (18) and a shallow circumferential groove (19) provided with a non-contact seal portion (17) and a pressurized space (16) at one bearing end of a hydrostatic air radial bearing. Shows a comparative example in which is provided near the other bearing end.
[0020]
FIG. 5 shows a comparative example in which a pressurized space (21) and a non-contact seal portion (20) are provided on the outer side of the hydrostatic thrust bearing (24), and an air supply throttle (23) is provided closer to the inner diameter side. . It is desirable to connect the pressurizing space (21) and the pressure adjusting means (not shown) via the air pipe (22) so that the pressure in the pressurizing space (21) is kept constant.
[0021]
Next, a case where a plurality of hydrostatic air bearings are arranged adjacent to each other will be described. In this case, since each bearing gap has an effect as a non-contact seal portion, it is not recognized that a special non-contact seal portion is required.
[0022]
FIG. 6 shows an embodiment in which a circumferential groove-shaped space (27) between two adjacent hydrostatic air radial bearings (28) and (29) is formed as a pressurized space.
[0023]
FIG. 7 shows a case where a pressurized space (32) is provided on the outer side of the double-sided opposed static pressure air thrust bearings (30), (31). In a double-sided hydrostatic thrust bearing, the change in pressure due to shaft displacement is reversed (when one pressure increases, the other decreases), the pressure space (32) on both sides is reduced. The generation of self-excited vibration is suppressed by sharing the pressure and suppressing the pressure change in the pressurizing space (32). As indicated by a dotted line in FIG. 7, in this comparative example, it is also possible to provide a pressure adjusting means for the pressurizing space (32).
[0024]
In FIG. 8, a pressurizing space (39) is provided between adjacent thrust bearings (38) and radial bearings (37), and an air supply line (40) communicating the pressurizing space (39) and the pressure adjusting means. ) (41) (42) is shown.
[0025]
9 and 10 show an embodiment in which the present invention is applied to a static pressure air bearing type linear motion guide device. FIG. 10 is a view taken along line XX in FIG. In the case of a linear guide device, a plurality of bearings (43) (49) divided by grooves are often provided on the moving table side so as to face one surface of the fixed guide member. Compressed air is supplied to these bearing portions from the bearing air supply pipe (44). By providing the non-contact seal portions (45) and (48) so as to surround these bearings, a pressurized space can be configured. Further, the pressurizing spaces on each surface are connected to a pressure adjusting means (not shown) via the air pipe (47), and the pressure in each pressurizing space is maintained at a constant value.
[0026]
According to the present invention, since the average pressure of the bearing gap can be increased without using a groove or the like, vibration damping performance is better than that of a conventional hydrostatic air bearing, and it is highly resistant to disturbances. A hydrostatic air bearing device is provided.
[0027]
FIG. 11 shows a hydrostatic air thrust bearing to which the present invention is applied. FIG. 12 shows a partially enlarged longitudinal sectional view thereof. Radial bearings (52) (53) and thrust bearings (54) (55) have shallow circumferential grooves (60) that communicate with fine throttle holes (56) (57) (58) (59) that open in the bearing gap. ) (61) (62) (63) are provided, and when compressed air is supplied via the bearing air supply lines (64) (65) (66), etc., the main shaft (51) Supported in contact. Compressed air flowing out from each bearing gap is discharged out of the hydrostatic air bearing via the exhaust holes (67) and (68). In the pressurized space (69) provided at the bearing clearance outlet of the thrust bearing (54) on the radial bearing side, the compressed air adjusted to a constant pressure is supplied to the air supply line separately from the bearing air supply pipe. Supplied through (70) (71). The air supply pipe (71) is provided at a plurality of locations along the circumferential direction in order to ensure a sufficient flow path area to keep the internal pressure of the pressurized space (69) equal to the supply pressure of the compressed air. For this reason, the internal pressure of the pressurizing space (69) becomes higher than the ambient atmospheric pressure, and the pressure in the bearing gap increases accordingly, so that the bearing reaction force of the thrust bearing (54) increases. As a result, the thrust plate (72) of the main shaft moves to the thrust bearing (55) side and stops at a position where the bearing reaction forces of the thrust bearings (54) and (55) on both sides are balanced. Therefore, the bearing clearance of the thrust bearing (55) can be set much narrower than before, and if the type and dimensions of the throttle are selected corresponding to this narrow bearing clearance, the bearing support rigidity In addition, vibration damping performance can be dramatically improved. In addition, the thrust bearing (54) has a wider bearing clearance, but the average pressure in the bearing clearance is higher, so the vibration damping coefficient does not decrease much, and it is supported by optimizing the dimensions of the throttle valve. It is possible to suppress the decrease in rigidity and damping coefficient to the minimum. Therefore, the present invention greatly contributes to the improvement of the support rigidity and vibration damping coefficient of the two thrust bearings (54) and (55), and can realize a highly accurate hydrostatic air bearing device. The thrust bearing (54) on the side where the outlet pressure of the bearing gap is increased, even when the supply air pressure is increased, the pressure on the outlet side of the bearing gap is increased proportionally, so that the vibration damping coefficient is the same as the conventional one. Since substantially the same level can be maintained, a particularly remarkable effect is recognized when the bearing supply air pressure is increased to improve performance.
[0028]
FIG. 11 illustrates an embodiment in which compressed air having a constant pressure is supplied to the pressurized space (69). However, the internal pressure of the pressurized space (69) can be set higher than the ambient atmospheric pressure by restricting bearing exhaust. Can also be maintained at high pressure. In this case, an appropriate throttle valve is interposed in the air supply line (70), and the bearing exhaust is discharged to the outside of the hydrostatic air bearing device via the throttle valve.
[0029]
As for the throttle type of the bearing, FIG. 11 illustrates an embodiment in which a composite throttle comprising a throttle hole and a shallow groove provided on the bearing surface is used as the pressure adjusting means of the pressurizing space (69). In addition, a self-contained diaphragm, an orifice diaphragm, a slot diaphragm, a porous diaphragm, etc., which are generally used in a hydrostatic air bearing device can be used.
[0030]
FIG. 13 shows an embodiment in which the internal pressure of the pressurizing space (82) on the inner peripheral side of the thrust bearing (81) opposite to the radial bearing is increased to narrow the bearing clearance of the thrust bearing (84) on the radial bearing side. Show. The pressurizing space (82) is connected to a pressure adjusting means (not shown) via an air supply line (83). As the pressure adjusting means, either a compressed air source adjusted to a constant pressure or a throttle valve for restricting bearing exhaust from the pressurized space (82) can be used.
[0031]
FIG. 14 shows a double-sided opposed static pressure air thrust bearing of the type in which the housing (93) is sandwiched between two thrust plates (91) and (92), and a small gap is formed on the outer periphery of one thrust bearing (94). The pressurizing space (96) is configured using the non-contact portion (95) due to the above, thereby reducing the bearing gap of the other thrust bearing (97).
[0032]
【The invention's effect】
According to the present invention, since the average pressure of the bearing gap can be increased without using a groove or the like, the vibration damping performance is better than that of the conventional hydrostatic air bearing device, and high-accuracy static pressure is strong against disturbance. An air bearing device is obtained.
[0033]
Further, when the present invention is applied to a double-sided opposed static air thrust bearing device, the bearing rigidity and vibration damping coefficient of the thrust bearing can be reduced by reducing one bearing gap of the thrust bearing and increasing the other bearing gap pressure. A large high precision hydrostatic thrust bearing device is obtained. In addition, since the total value of both thrust bearing gaps is maintained at the same level as that of the conventional bearing device, it is easy to manage the dimensions of the bearing constituent members. Furthermore, even when the dimensions related to the bearing gap change due to thermal deformation, the bearing with the smaller gap retains high rigidity, so almost all of the change in dimensions is absorbed by the bearing with the larger gap. Is done. As a result, contact between the bearing and the thrust plate is avoided, and a highly reliable double-sided opposed static air thrust bearing device with stable performance is provided.
[0034]
Further, since the bearing characteristics can be changed by adjusting the internal pressure of the pressurizing space, it is possible to set the optimum bearing characteristics corresponding to the change in operating conditions.
[Brief description of the drawings]
FIG. 1A is a partial longitudinal sectional view of a hydrostatic air bearing device showing an embodiment of the present invention, and FIG. 1B is a pressure distribution diagram.
FIG. 2 is a partial longitudinal sectional view showing another embodiment.
FIG. 3 is a partial longitudinal sectional view showing a comparative example .
FIG. 4 is a partial longitudinal sectional view showing a comparative example .
FIG. 5 is a partial longitudinal sectional view showing a comparative example .
FIG. 6 is a partial longitudinal sectional view showing another embodiment.
FIG. 7 is a partial longitudinal sectional view showing a comparative example .
FIG. 8 is a partial longitudinal sectional view showing another embodiment.
FIG. 9 is a longitudinal sectional view showing another embodiment.
10 is a view as seen from the line XX in FIG. 9. FIG.
FIG. 11 is a longitudinal sectional view showing another embodiment.
FIG. 12 is a partially enlarged view of FIG.
FIG. 13 is a longitudinal sectional view showing another embodiment.
FIG. 14 is a longitudinal sectional view showing another embodiment.
[Explanation of symbols]
3 Bearing clearance 5, 5 ', 16, 21, 27, 32, 39 Pressurizing space 6, 6', 17, 20, 45, 48 Non-contact seal

Claims (2)

  Bearing surfaces facing each other are provided on the fixed portion and the movable portion, and compressed air is supplied to the bearing gap formed between the two bearing surfaces via an air supply throttle so that the movable portion is not in contact with the fixed portion. In a hydrostatic air bearing held in contact, the pressure of the compressed air introduced into the bearing gap and on the both sides in the axial direction of the bearing gap is set higher than the ambient atmospheric pressure. A static pressure air bearing device in which a pressurized space is formed, an air supply line communicating with the pressure space is provided on the fixed portion side, and the air supply line is connected to a compressed air source via a pressure adjusting means.   In a hydrostatic thrust bearing device having a double-sided opposed thrust plate, the fixed portion of the bearing member and the movable main shaft member are movable adjacent to the bearing clearance outlet provided on the inner or outer peripheral side of the thrust plate. A pressurized space that is isolated from the outside of the bearing device through a bearing gap and a non-contact seal portion, and the pressurized space from the compressed air source to the inlet portion of the bearing gap. A static pressure air bearing device in which an air supply line for introducing compressed air is connected to the air supply line, and a means for adjusting the compressed air pressure flowing into the pressurized space is provided in the air supply line.

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