WO2011089752A1 - 静圧軸受装置および静圧軸受装置を備えたステージ - Google Patents
静圧軸受装置および静圧軸受装置を備えたステージ Download PDFInfo
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- WO2011089752A1 WO2011089752A1 PCT/JP2010/065709 JP2010065709W WO2011089752A1 WO 2011089752 A1 WO2011089752 A1 WO 2011089752A1 JP 2010065709 W JP2010065709 W JP 2010065709W WO 2011089752 A1 WO2011089752 A1 WO 2011089752A1
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- groove
- bearing device
- orifice
- pressurized gas
- hydrostatic bearing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C32/00—Bearings not otherwise provided for
- F16C32/06—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C32/00—Bearings not otherwise provided for
- F16C32/06—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings
- F16C32/0603—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings supported by a gas cushion, e.g. an air cushion
- F16C32/0614—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings supported by a gas cushion, e.g. an air cushion the gas being supplied under pressure, e.g. aerostatic bearings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C29/00—Bearings for parts moving only linearly
- F16C29/02—Sliding-contact bearings
- F16C29/025—Hydrostatic or aerostatic
Definitions
- the present invention relates to a high-accuracy hydrostatic bearing device and a stage equipped with a hydrostatic bearing device that floats, supports, and moves a moving body with respect to a fixed body by pressurized gas.
- FIG. 9 shows an example of a conventional hydrostatic bearing device.
- the hydrostatic bearing device 100 is formed so as to surround the fixed body 120 and the fixed body 120 formed in a prismatic shape, and is configured to be movable along the fixed body 120.
- FIG. 9B is an enlarged sectional view taken along line XX of FIG. 9A.
- a discharge port 111a that communicates with a pressurized gas supply source and discharges the pressurized gas, and the pressurized gas discharged from the discharge port 111a is distributed along the sliding surface 110a.
- a static pressure pad 111 having a ventilation groove 111b is formed.
- the ventilation groove 111b is formed in a rectangular cross-sectional groove having a groove depth of about 30 ⁇ m and a groove width of 1000 ⁇ m.
- pressurized gas is discharged from the hydrostatic pad 111 into the bearing gap G ⁇ b> 1 formed between the sliding surface 110 a of the moving body 110 and the fixed body 120, thereby moving the moving body 110 to the fixed body 120. It can be lifted up and moved along the extending direction of the fixed body 120.
- the hydrostatic bearing device 100 is a moving mechanism in which the moving body 110 and the fixed body 120 are not in contact with each other, vibration is hardly generated and high-precision positioning is possible.
- the vibration of the moving body is caused by the pressurized gas flowing through the bearing gap G1 becoming unstable.
- the pressurized gas has a stable flow in both the laminar flow region and the turbulent flow region, but in the intermediate region between them, the pressure fluctuation of the gas becomes intense and the flow becomes unstable.
- Patent Document 1 discloses a flow path forming technique in which a turbulent flow is less likely to occur by improving the flow path pattern shape of the ventilation groove.
- Patent Document 2 discloses a technique that reduces the viscosity resistance of the gas flow by reducing the surface roughness of the sliding surface of the static pressure pad and does not generate turbulent flow.
- Patent Document 3 the turbulent flow is stabilized by eliminating the transition between turbulent flow and laminar flow by roughening the gas outflow part of the sliding surface of the static pressure pad with the idea opposite to Patent Document 1 or 2.
- a technique for preventing a vibration by forming a basin is disclosed.
- Patent Document 1 Japanese Patent Laid-Open No. 2003-194059
- Patent Document 2 Japanese Patent Laid-Open No. 6-307449
- Patent Document 3 Japanese Patent No. 3260869
- the surface roughness of the sliding surface is made rough as in the technique described in Patent Document 3, and the turbulent flow is positively performed. May form an intermediate region between laminar flow and turbulent flow. Since the vibration caused by the turbulent flow does not have a specific frequency and has a wide frequency of 10 to several tens of kHz, the resonance frequency of the hydrostatic bearing device cannot be excluded from the frequency band of the minute vibration. When the hydrostatic bearing device resonates due to this minute vibration, the vibration amplitude may increase to several 100 nm.
- the present invention reduces the occurrence of vibration by configuring an orifice, a ventilation groove, and the like so that a laminar flow state is maintained in the entire region of the ventilation path of the pressurized gas based on the supply air pressure to be applied.
- An object of the present invention is to realize a high-precision hydrostatic bearing device that can be prevented and a stage including the hydrostatic bearing device.
- a bearing gap is provided between the sliding surfaces of the fixed body and the movable body, and pressurized gas is supplied to the bearing gap.
- the hydrostatic bearing device is configured to float and move on the fixed body, and the movable body includes a main pipe that supplies pressurized gas and a main pipe that opens to a sliding surface.
- An orifice provided at the discharge port for rectifying the pressurized gas; and a static pressure pad formed with a ventilation groove communicating with the orifice and distributing and supplying the pressurized gas discharged from the orifice to the bearing gap;
- the ventilation groove includes an annular groove formed in an annular shape surrounding the orifice, and a plurality of holes extending radially toward the annular groove around the orifice and communicating the annular groove and the orifice.
- a distribution groove, and the transfer groove The technical means is formed so as to be symmetric with respect to the moving direction center line of the moving body, and the cross-sectional shape in the width direction of the ventilation groove forms a convex curve away from the sliding surface. Use.
- the pressurized gas is supplied by the main pipe provided in the moving body, and the pressurized gas is rectified by the orifice provided in the discharge port of the main pipe that opens on the sliding surface.
- the bearing gap provided between the sliding surfaces of the fixed body and the moving body by a static pressure pad formed with a ventilation groove communicating with the orifice and supplying pressurized gas discharged from the orifice to the bearing gap.
- the ventilation groove includes an annular groove formed in an annular shape surrounding the orifice, and a plurality of distribution grooves extending radially toward the annular groove around the orifice and communicating the annular groove and the orifice,
- the pressurized gas discharged from the hydrostatic pad to the bearing gap can be made into a laminar flow with a uniform pressure distribution, so that a highly accurate hydrostatic bearing device capable of preventing the occurrence of vibration can be realized. it can. Furthermore, since the laminar flow can be stably maintained, the supply pressure of the pressurized gas can be increased, so that a highly rigid hydrostatic bearing device can be realized.
- the sum of the cross-sectional areas in the width direction of the distribution grooves is equal to or larger than the cross-sectional area of the orifice.
- the cross-sectional area of the orifice Since the relationship of S1 ⁇ n ⁇ S2 is established with S2, pressure loss is unlikely to occur when the pressurized gas discharged from the orifice flows into the distribution groove, so that a stable laminar flow can be maintained. And the occurrence of vibrations can be prevented.
- the surface roughness of the ventilation groove is formed to be smaller than the surface roughness of the sliding surface of the movable body.
- the surface roughness of the ventilation groove is formed to be smaller than the surface roughness of the sliding surface of the moving body, the flow of the pressurized gas compared to the sliding surface In the ventilation groove that tends to transition to turbulent flow, it is possible to make it difficult for the flow to be disturbed due to surface roughness, so that a stable laminar flow can be maintained and the occurrence of vibration can be prevented.
- the surface roughness Ra (arithmetic average roughness) of the sliding surface is 0.2 to 0.6 ⁇ m
- the surface roughness Ra of the ventilation groove is preferably 0.1 to 0.4 ⁇ m.
- the annular groove is provided so as to surround from the ventilation groove to the bearing gap.
- An exhaust groove that guides and discharges the supplied pressurized gas to the outside of the bearing gap, and is formed so as to be symmetric with respect to the moving direction center line of the moving body, and has a cross section in the width direction.
- a technical means is used in which an exhaust groove having a convex curve in a direction away from the sliding surface and having a cross-sectional area equal to or larger than the cross-sectional area of the annular groove is used.
- the pressure distribution of the pressurized gas can be efficiently exhausted outside the bearing gap so that the pressure distribution of the pressurized gas becomes uniform, and the flow rate of the pressurized gas can be stabilized. As a result, laminar flow can be stably maintained.
- the bearing gap is set to 10 ⁇ m or less in the hydrostatic bearing device according to any one of the inventions according to the first to third aspects.
- the laminar flow can be stably maintained, so that the bearing gap can be reduced.
- the hydrostatic bearing device can be configured such that the bearing gap is 10 ⁇ m or less, which is smaller than the bearing gap of the conventional hydrostatic bearing device. Thereby, it can be set as a more rigid hydrostatic bearing apparatus.
- the surface accuracy can be improved, so that a hydrostatic bearing device with higher rigidity and accuracy can be configured.
- ceramic has a low thermal expansion compared to a metal material, a dimensional change due to a temperature change can be reduced, so that a hydrostatic bearing device with higher accuracy can be realized.
- the stage includes the hydrostatic bearing device according to any one of the first to third aspects of the invention, and an object is mounted on the movable body along the fixed body.
- the technical means of being configured to be movable is used.
- the stage since the stage includes the hydrostatic bearing device according to any one of the first to third aspects of the invention, the stage has high rigidity and is driven and stabilized. It can be set as the favorable stage which suppressed generation
- FIG. 2 is an enlarged explanatory view of an AA cross section of FIG. 1
- FIG. 2B is an enlarged explanatory view of an orifice.
- FIG. 4 is a cross-sectional explanatory view showing a cross-sectional shape in the width direction of the ventilation groove and the exhaust groove, which is a BB cross section of FIG. 3.
- It is explanatory drawing which shows the relationship between the supply pressure of pressurized gas, and a consumption flow rate.
- FIG. 9A is a perspective explanatory view
- FIG. 9B is an enlarged explanatory view of the XX cross section of FIG. 9A.
- the hydrostatic bearing device 1 includes a fixed body 20 formed in a prismatic shape, and a movable body 10 formed so as to surround the fixed body 20 and movable along the fixed body 20. And consist of
- the moving body 10 and the fixed body 20 are made of ceramics such as alumina, for example. If the moving body 10 and the fixed body 20 are made of ceramics, the surface accuracy can be improved, so that turbulent flow is less likely to occur, and a highly accurate hydrostatic bearing device can be configured. In addition, since ceramic has a low thermal expansion compared to a metal material, a dimensional change due to a temperature change can be reduced, so that a highly accurate hydrostatic bearing device can be realized.
- the moving body 10 includes a main pipe 13 that supplies pressurized gas, an orifice 14 that rectifies the pressurized gas, and the pressurized gas discharged from the orifice 14 in communication with the orifice 14. And a hydrostatic pad 30 that distributes and supplies gas to a bearing gap G formed between the sliding surface 10a of the moving body 10 and the fixed body 20.
- the static pressure pad 30 is formed with a ventilation groove 11 composed of a distribution groove 11a and an annular groove 11b described later.
- An exhaust groove 12 is formed on the outer periphery of the ventilation groove 11 to guide and exhaust the pressurized gas supplied from the ventilation groove 11 to the bearing gap G to the outside of the bearing gap G.
- FIG. 2A the structure of the moving body 10 above the fixed body 20 is shown, but the same structure is formed on the lower sliding surface facing the fixed body 20 with the structure interposed therebetween.
- a similar structure may be formed on the horizontal sliding surface.
- the orifice 14 is provided in the discharge port 13a of the main pipe 13 that opens to the sliding surface 10a (the lower surface in the figure), and the discharge port 13a side has a tapered shape with little pressure loss. Is formed. Thereby, it rectifies
- the main pipe 13 is formed in a tubular shape with a diameter of about 3 to 5 mm, and the orifice 14 is formed with a tip diameter of 0.2 to 0.3 mm.
- a pressurized gas is supplied from the main pipe 13 through the orifice 14 to the hydrostatic pad 30, and is formed between the sliding surface 10 a of the moving body 10 and the fixed body 20 from the hydrostatic pad 30.
- the movable body 10 is levitated on the fixed body 20 and moved along the extending direction of the fixed body 20 and can be positioned with high accuracy.
- the pressurized gas discharged from the static pressure pad 30 to the bearing gap G is exhausted to the outside of the bearing gap G by the exhaust groove 12.
- the hydrostatic bearing device 1 of the present invention has an orifice 14, a ventilation groove 11, and an exhaust so that a laminar flow state is maintained in the entire area of the pressurized gas ventilation path.
- the configuration such as the shape of the groove 12 is designed. Hereinafter, a specific configuration will be described.
- the sliding surface 10a is formed in a rectangular shape, and a static pressure pad 30 provided with a ventilation groove 11 and an exhaust groove 12 are formed on the sliding surface 10a.
- the static pressure pad 30 is formed by a composite diaphragm that combines an orifice diaphragm and a surface diaphragm.
- the ventilation groove 11 has an annular groove 11b formed in an annular shape surrounding the orifice 14 and a plurality of distribution grooves that extend radially toward the annular groove 11b around the orifice 14 and communicate the annular groove 11b with the orifice 14. 11a.
- the annular groove 11b is formed in a circular shape, and 16 distribution grooves 11a are formed at a central angle of 22.5 °.
- the ventilation groove 11 is formed so as to be symmetric with respect to the moving direction of the moving body 10 (left and right direction in the figure).
- the exhaust groove 12 includes an annular exhaust groove 12a provided so as to surround the annular groove 11b, and an external exhaust groove 12b that communicates the annular exhaust groove 12a with the outside of the hydrostatic bearing device 1.
- the exhaust groove 12 is formed in a shape that allows efficient exhaust to the outside so that the pressure distribution of the pressurized gas is uniform (FIG. 4).
- the exhaust groove 12 is formed to be symmetric with respect to the moving direction center line of the moving body 10.
- the annular exhaust groove 12a is preferably similar to the annular groove 11b in order to exhaust an amount corresponding to the pressurized gas discharged from the annular groove 11b so that the pressure distribution is uniform.
- the circular groove 11b has a circular shape.
- the radius R2 of the annular exhaust groove 12a is not less than the radius R1 of the annular groove 11b and a space larger than twice the width W1 (FIG. 4) of the annular groove 11b is secured, pressure loss and pressurized gas It is possible to achieve a good exhaust state in which the flow of air is not disturbed.
- R2 ⁇ R1 2 to 10 mm, but good exhaust is possible and no vibration is generated.
- the pressurized gas discharged from the main pipe 13 through the orifice 14 through the discharge port 13a is isotropically distributed in the static pressure pad 30 by the distribution groove 11a, and is distributed from the distribution groove 11a and the annular groove 11b to the bearing gap G.
- the exhaust groove 12 exhausts the outside of the bearing gap G.
- the pressure distribution of the pressurized gas in the bearing gap G can be made uniform by forming the ventilation groove 11 so as to be symmetric with respect to the moving direction center line of the moving body 10. Further, by providing the exhaust groove 12, the pressurized gas can be efficiently exhausted to the outside so that the pressure distribution of the pressurized gas becomes uniform, and the flow rate of the pressurized gas can be stabilized.
- the vent groove 11 (only the annular groove 11b is shown in the figure) and the exhaust groove 12 (only the annular exhaust groove 12a is shown in the figure) have a cross-sectional shape in the width direction away from the sliding surface 10a.
- a convex curve is formed.
- the annular groove 11b has an arcuate cross section, and is formed so that the depth D1 is 10 ⁇ m or less and the width W1 is 300 to 500 ⁇ m.
- the distribution groove 11a has a similar cross-sectional shape.
- the ventilation groove 11 can be formed, for example, by processing with a grinding drill having a radius of 1 to 5 mm.
- the pressurized gas flows out from the width direction of each groove to the bearing gap G. In this case, there is no pressure loss or air current turbulence, and laminar flow can be maintained.
- the sum of the cross-sectional areas in the width direction of the distribution grooves 11a is formed to be equal to or larger than the cross-sectional area of the orifice 14.
- the cross-sectional area of the distribution groove 11a is S1
- there are 16 distribution grooves 11a so the relationship of S1 ⁇ 16 ⁇ S2 is established with the cross-sectional area S2 of the orifice 14.
- the exhaust groove 12 is preferably equal to or larger than the cross-sectional area of the annular groove 11b in order for the annular exhaust groove 12a to exhaust an amount corresponding to the pressurized gas discharged from the annular groove 11b.
- the cross-sectional shape of the annular groove 11b is an arc shape like the ventilation groove 11, and the depth D2 is 30 ⁇ m and the width W2 is 300 ⁇ m.
- the corner of the boundary between the sliding surface 10a and the ventilation groove 11 or the exhaust groove 12 is chamfered and formed smoothly, the flow can be made more difficult to disturb, and the laminar flow state is stabilized. be able to.
- the surface roughness of the ventilation groove 11 is formed to be smaller than the surface roughness of the sliding surface 10 a of the moving body 10. Therefore, in the ventilation groove 11 in which the flow of the pressurized gas is likely to transition to the turbulent flow compared to the sliding surface 10a, it is possible to make it difficult for the flow turbulence due to the surface roughness to occur. Can be maintained, and the occurrence of vibrations can be prevented.
- the surface roughness Ra (arithmetic mean roughness) of the sliding surface 10a is 0.2 to 0.6 ⁇ m
- the surface roughness Ra of the ventilation groove 11 is preferably 0.1 to 0.4 ⁇ m.
- the laminar flow can be stably maintained, and high rigidity can be obtained even when the supply pressure of the pressurized gas is lowered. Therefore, by reducing the bearing gap G so as to be 10 ⁇ m or less, which is smaller than the bearing gap of the conventional hydrostatic bearing device, a more rigid hydrostatic bearing device can be obtained.
- the hydrostatic bearing device 1 of the present invention has the above-described configuration, the pressurized gas discharged from the hydrostatic pad 30 to the bearing gap G can be made into a laminar flow with a uniform pressure distribution. It is possible to realize a hydrostatic bearing device 1 that can perform high-precision positioning that can prevent occurrence, for example, ultra-high-precision positioning of 10 nm or less. Furthermore, since the laminar flow can be stably maintained, the supply pressure of the pressurized gas can be increased, and thus the highly rigid hydrostatic bearing device 1 can be realized.
- the stage which mounts an object on the moving body 10 using the hydrostatic bearing device 1 and is movable along the fixed body 20 is configured, it is highly rigid and suppresses the generation of vibrations during driving and in a static state.
- the stage provided with the hydrostatic bearing device 1 can be suitably used for applications requiring high traveling accuracy, such as a scanning exposure apparatus and a liquid crystal panel inspection apparatus.
- a multi-axis moving mechanism such as an XY stage can be formed by combining a plurality of hydrostatic bearing devices.
- the cross-sectional shape of the ventilation groove 11 and the exhaust groove 12 is a convex shape with a smooth curve and can achieve a laminar flow, an elliptical arc or other curved shape can be adopted.
- the arrangement shape of the ventilation groove 11 and the exhaust groove 12 may be symmetric with respect to the moving direction center line, and may be asymmetric in the direction perpendicular to the moving direction.
- the number of distribution grooves 11a and external exhaust grooves 12b is arbitrary as long as the laminar flow can be maintained.
- the cross-sectional shape of the distribution groove 11a and the cross-sectional shape of the annular groove 11b, or the cross-sectional shape of the annular exhaust groove 12a and the cross-sectional shape of the external exhaust groove 12b can be different as long as the laminar flow can be maintained. .
- the exhaust groove 12 may not be provided.
- various ceramics such as zirconia, silicon carbide, and silicon nitride can be used in addition to alumina. Moreover, it can also form with materials other than ceramics, for example, metal materials, such as stainless steel.
- a rectangular column made of alumina ceramics having a purity of 99.8 %% and having a cross section of 42 mm ⁇ 42 mm and a length of 200 mm was used as the fixed body 20.
- the moving body 10 was configured by combining four flat plates so as to surround the fixed body 20 with the same alumina ceramic.
- the upper and lower flat plates have a width of 80 mm, a thickness of 20 mm, and a length of 80 mm.
- the left and right flat plates are a flat plate having a width of 40 mm, a thickness of 20 mm, and a length of 80 mm.
- Bearing mechanisms such as the static pressure pad 30 and the exhaust groove 12 are provided on the sliding surfaces 10a of the upper and lower flat plates.
- the orifice 14 has a tip diameter of 0.3 mm.
- the ventilation groove 11 is formed so that the cross section in the width direction has an arc shape with a depth of 10 ⁇ m and a width of 300 ⁇ m.
- the bearing gap G was 2 ⁇ m.
- the sliding surface 10a has a surface roughness Ra of 0.4 ⁇ m, and the ventilation groove 11 has a surface roughness Ra of 0.2 ⁇ m or less.
- the consumption flow rate of the pressurized gas was evaluated.
- the consumption flow rate is evaluated by measuring the amount of gas consumed by the compressed air discharged from the exhaust groove 12 and the bearing gap G when the supply pressure of the compressed air supplied from the main pipe 13 is changed. It was.
- FIG. 5 is a measurement result of the consumption flow rate when the supply air pressure is changed in the range of 0.1 to 0.5 MPa.
- the consumption amount of compressed air is reduced to about 2/3 that of the conventional hydrostatic bearing device, and the effect of reducing the consumption amount of compressed air was confirmed.
- the bearing rigidity was evaluated.
- the bearing rigidity was calculated by the following equation by measuring the amount of displacement that the moving body 10 sinks when a predetermined load is applied to the moving body 10 with an electric micrometer.
- FIG. 6 shows the measurement results of the bearing rigidity when the supply air pressure is changed in the range of 0.1 to 0.5 MPa.
- the bearing rigidity is about 1.6 times higher than that of the conventional hydrostatic bearing device, and in combination with the result shown in FIG. It was confirmed that this was a highly rigid hydrostatic bearing device.
- FIG. 7 shows the measurement results of the vibration amplitude when the supply air pressure is changed in the range of 0.1 to 0.5 MPa. Until the supply pressure is up to 0.2 MPa, vibration hardly occurs in both cases. However, when it exceeds 0.3 MPa, the vibration amplitude becomes large in the conventional hydrostatic bearing device, and the vibration amplitude level becomes unusable at 0.5 MPa. On the other hand, in the hydrostatic bearing device 1 of the present invention, vibration hardly occurred even at 0.5 MPa. As described above, the hydrostatic bearing device 1 and the optimum setting of the present invention can stably operate the hydrostatic bearing device 1 at a vibration amplitude level of 10 nm or less.
- the orifice 14 is maintained so that the laminar flow state is maintained in the entire region of the ventilation path of the pressurized gas.
- the structure of the ventilation groove 11 and the exhaust groove 12 is designed, and the cross-sectional shape in the width direction of the ventilation groove 11 forms a convex curve in the direction away from the sliding surface 10a.
- the ventilation groove 11 includes an annular groove 11b formed in an annular shape surrounding the orifice 14 and a plurality of holes extending radially toward the annular groove 11b around the orifice 14 and communicating the annular groove 11b and the orifice 14 with each other.
- the pressurized gas discharged from the hydrostatic pad 30 to the bearing gap G can be made into a laminar flow with a uniform pressure distribution, so that a highly accurate hydrostatic bearing device 1 that can prevent the occurrence of vibration is realized. can do. Furthermore, since the laminar flow can be stably maintained, the supply pressure of the pressurized gas can be increased, and thus the highly rigid hydrostatic bearing device 1 can be realized.
- the single configuration of the static pressure pad 30 is adopted.
- the configuration is not limited to this, and a configuration in which a plurality of static pressure pads 30 are provided on one sliding surface 10a may be employed. it can.
- four static pressure pads 30 can be arranged symmetrically.
- the exhaust groove 12 in addition to the annular exhaust groove 12a and the external exhaust groove 12b, the second is formed in a cross so as to partition the region where the static pressure pad 30 is formed and communicates with the external exhaust groove 12b to assist the exhaust.
- An external exhaust groove 12c is formed.
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Abstract
Description
特許文献2には、静圧パッドの摺動面の表面粗さを小さくすることにより、気体が流れる粘性抵抗を小さくし、乱流を発生させない技術が開示されている。
特許文献3には、特許文献1または2と逆の発想で、静圧パッドの摺動面の気体流出部を粗面化することにより、乱流と層流との遷移をなくして安定した乱流域を形成して、振動を防止する技術が開示されている。
特許文献2: 特開平6-307449号公報
特許文献3: 特許3260869号公報
特許文献2に記載の技術のように静圧パッドの摺動面の表面粗さRaを0.1μm以下の非常に平滑な面に加工すると製造コストが増大するという問題があった。
また、移動体と固定体との軸受間隙は移動体の走行中に変化しやすいため、特許文献3に記載の技術のように摺動面の表面粗さを荒くして、積極的に乱流を形成しても層流と乱流との中間領域になってしまうことがある。乱流により生じる振動は固有の振動数を持たず10~数10kHzという幅広い周波数の振動であるため、静圧軸受装置の共振周波数をこの微小振動の周波数の帯域外に外すことはできない。この微小振動により静圧軸受装置が共振した場合には、数100nmの振動振幅に増大することも起きうる。
ここで、通気溝の幅方向の断面形状が摺動面から離れる方向に凸の曲線を形成しているため、加圧気体が通気溝の幅方向から軸受間隙に流れ出る際に、圧力損失や気流の乱れがなく、層流を維持することができる。
また、通気溝を、オリフィスを囲み環状に形成された環状溝と、オリフィスを中心に環状溝に向かって放射状に延設され、前記環状溝と前記オリフィスとを連通する複数の分配溝とから、移動体の移動方向中心線に対して対称となるように形成することにより、軸受間隙における加圧気体の圧力分布を一様にすることができる。
これらにより、静圧パッドから軸受間隙へ吐出される加圧気体を圧力分布が一様な層流とすることができるので、振動の発生を防止できる高精度な静圧軸受装置を実現することができる。
更に、層流を安定して維持することができるため、加圧気体の給気圧力を上げることができるので、高剛性の静圧軸受装置を実現することができる。
また、セラミックスは金属材料に比べて低熱膨張であるため、温度の変化による寸法変化を小さくすることができるので、より高精度の静圧軸受装置を実現することができる。
ここで、環状排気溝12aの半径R2は、環状溝11bの半径R1に加えて環状溝11bの幅W1(図4)の2倍以上大きい間隔が確保されていれば、圧力損失や加圧気体の流れが乱れることのない良好な排気状態とすることができる。後述する実施例では、R2-R1=2~10mmとしたが、良好な排気が可能であり、振動は発生しなかった。
本実施形態では、環状溝11bの断面形状は円弧状であり、深さD1は10μm以下、幅W1は300~500μmとなるように形成されている。分配溝11aも同様の断面形状を有している。通気溝11は、例えば、半径1~5mmの研磨ドリルなどで加工することにより形成可能である。
ここで、通気溝11及び排気溝12の幅方向の断面形状が摺動面10aから離れる方向に凸の曲線を形成しているため、加圧気体が各溝の幅方向から軸受間隙Gに流れ出る際に、圧力損失や気流の乱れがなく、層流を維持することができる。
例えば、摺動面10aの表面粗さRa(算術平均粗さ)が0.2~0.6μmの場合、通気溝11の表面粗さRaは0.1~0.4μmであることが好ましい。
更に、層流を安定して維持することができるため、加圧気体の給気圧力を上げることができるので、高剛性の静圧軸受装置1を実現することができる。
また、複数の静圧軸受装置の組み合わせにより、X-Yステージなどの多軸の移動機構を形成することもできる。
本発明の静圧軸受装置1の効果を、従来の静圧軸受装置100と比較した。
以上の通り、本発明の静圧軸受構造と最適設定により、静圧軸受装置1を10nm以下の振動振幅レベルで安定に作動させることができる。
(1)本発明の静圧軸受装置1によれば、高精度な移動、位置決めを実現するために、加圧気体の通気経路の全領域で層流状態が維持されるように、オリフィス14、通気溝11及び排気溝12の形状などの構成を設計したものであり、通気溝11の幅方向の断面形状が摺動面10aから離れる方向に凸の曲線を形成しているため、加圧気体が通気溝11の幅方向から軸受間隙に流れ出る際に、圧力損失や気流の乱れがなく、層流を維持することができる。
また、通気溝11を、オリフィス14を囲み環状に形成された環状溝11bと、オリフィス14を中心に環状溝11bに向かって放射状に延設され、環状溝11bとオリフィス14とを連通する複数の分配溝11aとから、移動体10の移動方向中心線に対して対称となるように形成することにより、軸受間隙Gにおける加圧気体の圧力分布を一様にすることができる。
排気溝12を設けることにより、加圧気体の圧力分布が一様になるように、軸受間隙G外へ効率よく排気でき、加圧気体の流量を安定させることができるので、層流を安定して維持することができる。
これらにより、静圧パッド30から軸受間隙Gへ吐出される加圧気体を圧力分布が一様な層流とすることができるので、振動の発生を防止できる高精度な静圧軸受装置1を実現することができる。
更に、層流を安定して維持することができるため、加圧気体の給気圧力を上げることができるので、高剛性の静圧軸受装置1を実現することができる。
10 移動体
10a 摺動面
11 通気溝
11a 分配溝
11b 環状溝
12 排気溝
12a 環状排気溝
12b 外部排気溝
12c 第2外部排気溝
13 主配管
13a 吐出口
14 オリフィス
20 固定体
30 静圧パッド
G 軸受間隙
Claims (7)
- 固定体と移動体との摺動面間に軸受間隙を設け、当該軸受間隙に加圧気体を供給することにより前記移動体を前記固定体上で浮上させ、移動可能に構成された静圧軸受装置であって、
前記移動体は、
加圧気体を供給する主配管と、
摺動面に開口する主配管の吐出口に設けられ、加圧気体を整流するオリフィスと、
前記オリフィスに連通し前記オリフィスから吐出された加圧気体を前記軸受間隙に分配して供給する通気溝が形成された静圧パッドと、を備え、
前記通気溝は、
前記オリフィスを囲み環状に形成された環状溝と、
前記オリフィスを中心に前記環状溝に向かって放射状に延設され、前記環状溝と前記オリフィスとを連通する複数の分配溝と、からなり、
前記移動体の移動方向中心線に対して対称となるように形成されており、
前記通気溝の幅方向の断面形状が摺動面から離れる方向に凸の曲線を形成していることを特徴とする静圧軸受装置。 - 前記分配溝の幅方向の断面積の総和が、前記オリフィスの断面積以上であることを特徴とする請求項1に記載の静圧軸受装置。
- 前記通気溝の表面粗さが前記移動体の摺動面の表面粗さよりも小さくなるように形成されていることを特徴とする請求項1に記載の静圧軸受装置。
- 前記環状溝を囲んで設けられ、前記通気溝から前記軸受間隙に供給された加圧気体を前記軸受間隙の外方に案内して排気する排気溝であって、
前記移動体の移動方向中心線に対して対称となるように形成されており、
幅方向の断面形状が摺動面から離れる方向に凸の曲線を形成しているとともに、断面積が前記環状溝の断面積以上である排気溝を備えたことを特徴とする請求項1ないし請求項3のいずれか1つに記載の静圧軸受装置。 - 前記軸受間隙を10μm以下としたことを特徴とする請求項1ないし請求項3のいずれか1つに記載の静圧軸受装置。
- 前記移動体及び固定体はセラミックスからなることを特徴とする請求項1ないし請求項3のいずれか1つに記載の静圧軸受装置。
- 請求項1ないし請求項3のいずれか1つに記載の静圧軸受装置を備え、前記移動体に物体を搭載して前記固定体に沿って移動可能に構成されたことを特徴とするステージ。
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