JP5404296B2 - Gas bearing and positioning device - Google Patents

Description

  The present invention relates to a gas bearing used for a positioning device mounted on a precision machine tool, a precision measuring instrument, or a semiconductor exposure apparatus.

  In order to improve the performance of a positioning device mounted on a precision machine tool, a precision measuring instrument, or a semiconductor exposure apparatus, it is necessary to improve the performance of a bearing that supports a positioning object. When the required level of positioning accuracy is on the nanometer level, gas bearings having characteristics such as friction-free, dust-free and low heat generation are generally used.

  However, in the case of a gas bearing, when an external force such as vibration is applied to the positioning object, positioning becomes unstable, and it takes time until the vibration of the positioning object converges. Further, since the self-excited vibration occurs when the damping characteristic is negative at a frequency equal to the natural frequency of the vibration system including the gas bearing and the positioning object, it is difficult to improve the performance of the positioning device.

  Conventionally, in order to improve the damping characteristics, as disclosed in Patent Document 1, there is an apparatus in which an incompressible fluid such as water or oil is interposed in a bearing and the viscosity of the incompressible fluid is used. . In this configuration, the fixed portion that is the guide member is held in a non-contact manner by the compressed air ejected from the movable portion. A concave portion is formed in the fixed portion, and an incompressible fluid is interposed between the tip surface of the convex portion from the movable portion and the bottom surface of the concave portion. This incompressible fluid functions as a damper and improves damping characteristics.

  In addition, as disclosed in Patent Document 2, there is one in which an electrostatic repulsive force is generated between a slide shaft that is a fixed portion and a movable portion to improve the damping characteristics of the gas bearing. This is composed of a movable part supported by a gas bearing and electrodes disposed opposite to the fixed part, and a sensor for detecting the displacement of the gap between the fixed part and the movable part. This sensor detects the displacement of the gap between the fixed part and the movable part, and the electrode generates an electrostatic attractive force having a phase opposite to the phase of the residual vibration detected by the sensor. Vibration is suppressed by controlling the electrostatic attraction force.

  In addition, as disclosed in Patent Document 3, there is an example in which the non-breathable land portion is provided at the center portion of the static pressure gas bearing, thereby improving the damping characteristics due to the squeeze effect.

JP-A-4-107321 JP-A-5-300722 JP-A-10-169654

  However, the configuration disclosed in Patent Document 1 has a problem that heat generation increases due to contamination of the bearing surface by the incompressible fluid and friction of the incompressible fluid.

  In addition, the configuration of Patent Document 2 has the advantage that the fixed portion and the movable portion are supported in a non-contact manner and have low heat generation. On the other hand, in order to control vibration, electrodes and sensors are used. There was a problem that the structure was complicated and the structure was complicated.

  In the configuration disclosed in Patent Document 3, since the non-breathable land portion is arranged at the center portion of the bearing surface, the damping characteristic is improved with a simpler structure than the configurations of Patent Document 1 and Patent Document 2. There is an advantage. However, since the air-impermeable land portion and the air-permeable bearing surface are continuously connected in the same plane, gas flows into the air-impermeable land portion from the air-permeable bearing surface. As a result, there is a problem that a sufficient squeeze effect cannot be obtained and the attenuation characteristics are insufficient.

An object of this invention is to provide the gas bearing which can implement | achieve a high damping characteristic with a simpler structure than before , and the positioning apparatus provided with the gas bearing .

In order to achieve the above object, the gas bearing of the present invention jets gas into the bearing gap between the movable part and the fixed part, and in the gas bearing that supports the movable part with a gas film, jets gas into the bearing gap. A gas ejecting surface that is formed of a separate member from the movable portion and the fixed portion, and a bearing pad mounting hole is formed on one of the movable portion and the fixed portion to be coupled by bolt fastening. has a bearing pad protrudes before SL bearing gap, the protruding surface for forming a 40μm following squeeze gap than 0.1μm between the other of said fixed portion and said movable portion opposing the gas ejection face spaced apart from, and characterized in that and a protruding portion that is attached to the bearing pads.
Further, the gas bearing of the present invention has a gas ejection surface for ejecting gas into the bearing gap between the movable portion and the fixed portion, and in the gas bearing supporting the movable portion by a gas film. A projecting surface that forms a squeeze gap of 0.1 μm or more and 40 μm or less between the bearing pad having the bearing pad and one of the fixed part and the movable part facing each other, and the movable part and A projection part that is formed of a separate member from the fixed part and is spaced apart from the gas ejection surface and attached to the other of the movable part and the fixed part, and the projection surface of the projection part It is characterized by being divided into a plurality of regions in a lattice shape by grooves shallower than the height.

  By providing the projecting surface to the bearing gap at a site away from the gas ejection surface, a stable squeeze air film can be formed, and high damping characteristics due to the damper effect can be realized.

  Further, by determining the peripheral length of the protruding surface according to the natural frequency of the vibration system including the object supported by the gas bearing, it is possible to efficiently improve the damping characteristic.

The gas bearing by Example 1 is shown, (a) is the sectional drawing, (b) is a top view which shows arrangement | positioning of the bearing pad and protrusion surface in a bearing surface. The gas bearing by Example 2 is shown, (a) is the sectional drawing, (b) is a top view which shows arrangement | positioning of the bearing pad and protrusion surface in a bearing surface. The gas bearing by Example 3 is shown, (a) is the sectional drawing, (b) is a top view which shows arrangement | positioning of the bearing pad and protrusion surface in a bearing surface. The gas bearing by Example 4 is shown, (a) is the sectional drawing, (b) is the end elevation seen from the arrow A direction of (a). Only the bearing pad of the gas bearing by Example 5 is shown, (a) is the sectional drawing, (b) is a top view which shows arrangement | positioning of a gas ejection surface and a protrusion surface. It is a graph which shows the attenuation | damping characteristic in case a squeeze clearance gap is 5-40 micrometers. It is a graph which shows the attenuation | damping characteristic in case the circumference of a protrusion surface is 40-200 mm.

  As shown in FIG. 1, the bearing pad 2 is attached to the movable portion 1, and the gas is ejected from the gas ejection surface 3 of the bearing pad 2 into the bearing gap 5 between the movable portion 1 and the fixed portion 4. The movable part 1 is supported in a non-contact manner by a high-pressure gas film. The movable part 1 is integral with a positioning stage of a positioning device (not shown). The movable portion 1 has a projecting surface 6 that faces the fixed portion 4 at a portion spaced from the gas ejection surface 3, and the projecting surface 6 projects from the movable portion 1 into the bearing gap 5, and is 0. A gap (squeeze gap) of 1 μm or more and 40 μm or less is formed.

  When a disturbance is applied to the movable portion 1, a squeeze effect is generated in the gap between the protruding surface 6 and the fixed portion 4. The squeeze effect is that the time average of the pressure in the gap becomes higher than the surrounding pressure due to the periodic relative motion of the two opposing surfaces in the direction perpendicular to the surface. In particular, in the case of a gas, a phase lag is caused with respect to the gap fluctuation due to compressibility, so that the attenuation characteristic becomes high in a high frequency region. Usually, in order to use the squeeze effect, a squeezed air film is actively generated by a driving means such as a piezoelectric element. However, by forming a gap of 0.1 μm or more and 40 μm or less, it is practical in a high frequency region. The present inventor has found that a good damping effect can be obtained.

  In addition, the above-described squeezed air is used to solve the problem that the gas bearing causes self-excited vibration when the damping characteristic is negative at a frequency equal to the natural frequency of the vibration system including the gas bearing and the positioning object (positioning stage). This can be dealt with by improving the damping characteristics of the membrane.

  In FIG. 6, the gas in the gap between the protruding surface 6 and the fixed portion 4 is air, the area of the protruding surface 6 is 50 × 50 mm, and the distance (squeeze gap) between the protruding surface 6 and the fixed portion 4 is 5 to 40 μm. It is a graph which shows the attenuation characteristic in. In FIG. 6, since the attenuation rate depends on the relative velocity in the direction perpendicular to the plane caused by the compressibility of air, the attenuation effect is expressed as attenuation rate × frequency.

As can be seen from FIG. 6, when the squeeze gap is wide, the damping effect by the squeeze air film is reduced. In order to set the value of attenuation rate × frequency at which a practical attenuation effect is obtained to 0.1 N / μm / cm ² , the squeeze gap must be 40 μm or less.

  Although the squeeze gap is 0.1 μm or more due to manufacturing problems, if the manufacturing problem is solved, the squeeze gap should be narrow so long as the protruding surface 6 does not contact the fixed part 4 or the movable part 1. However, the damping effect is high.

  The circumferential length of the protruding surface 6 is determined according to the natural frequency of the vibration system including the positioning stage which is an object supported by the gas bearing. FIG. 7 is a graph showing the attenuation characteristics when the dimension of the bearing gap 5 is fixed and the circumferential length of the protruding surface 6 is changed from 40 to 200 mm.

  As can be seen from FIG. 7, when the peripheral length of the projecting surface 6 is shortened, the frequency at which the attenuation effect is obtained is increased. Therefore, if the circumferential length of the protruding surface 6 is appropriately set so as to increase the damping effect at a frequency equal to the natural frequency of the vibration system including the gas bearing, the generated vibration can be converged in a short time.

  The protruding surface 6 may have lubricity. The anti-galling property can be enhanced by forming the protruding surface 6 with a lubricious material. Thereby, it is possible to prevent galling at the time of touchdown due to a sudden trouble such as when the supply gas is stopped or a load larger than expected is applied. Here, the lubricating material is, for example, a material in which graphite is fixed by means such as adhesion, or a material in which DLC or molybdenum disulfide is coated on the protruding surface by means such as sputtering or plating. The gas ejection surface provided in the gas bearing may be a surface constituted by any one of a porous diaphragm, a self-contained diaphragm, an orifice diaphragm, and a slot diaphragm.

  FIG. 1 shows a first embodiment, in which a bearing pad 2 is attached to a movable part 1, and pressurized gas is ejected from a gas ejection surface 3 of the bearing pad 2 toward a fixed part 4. It is supported without contact through the bearing gap 5. The protruding surface 6 protrudes from the movable part 1 and faces the fixed part 4. The distance (squeeze gap) between the protruding surface 6 and the fixed portion 4 is configured to be 0.1 μm or more and 40 μm or less. In this embodiment, for ease of mounting, as shown in FIG. 1A, the projecting surface 6 is flush with the gas ejection surface 3, and as shown in FIG. 1B, they are spaced from each other. Adjacent to each other.

  When a disturbance is applied to the movable part 1, a squeezed air film is formed in the gap between the projecting surface 6 and the fixed part 4. The squeeze air film generates a pressure proportional to the relative speed in the direction perpendicular to the protruding surface 6. This has the same effect as a state in which high-frequency volume fluctuations are caused in the sealed compressive fluid, thereby improving the damping characteristics.

  FIG. 2 shows a second embodiment. As in the first embodiment, the bearing pad 2 is attached to the movable portion 1, and compressed air as pressurized gas is ejected from the gas ejection surface 3 of the bearing pad 2 toward the fixed portion 4. The bearing gap 5 is supported in a non-contact manner. The protruding surface 6 protrudes from the fixed portion 4 and is disposed to face the movable portion 1, and the distance (squeeze gap) from the movable portion 1 is configured to be 0.1 μm or more and 40 μm or less.

  In the first embodiment, the squeezed air film is generated in the gap between the protruding surface and the fixed portion. However, in this embodiment, the damping characteristic is generated by generating the squeezed air film in the gap between the protruding surface and the movable portion. Improve.

  FIG. 3 shows a third embodiment. As in the first embodiment, a bearing pad 2 is attached to the movable part 1, and pressurized gas is ejected from the gas ejection surface 3 of the bearing pad 2 toward the fixed part 4, and the movable part 1 has a bearing gap 5. It is supported in a non-contact manner. The protruding surface 6 is formed with a groove 6a that protrudes from the movable portion 1 and is divided into a lattice-shaped region.

  Each region of the projecting surface 6 divided into a lattice pattern by the grooves 6a is formed as an independent projecting surface so as to be surrounded by the ambient pressure of the bearing gap 5, and the distance between the projecting surface 6 and the fixing portion 4 (squeeze gap). ) Is configured to be 0.1 μm or more and 40 μm or less.

  This embodiment has an advantage of high attenuation characteristics per unit area because it is easy to manufacture a projecting surface having a required circumference and the projecting surfaces can be arranged with high density.

  FIG. 4 shows a fourth embodiment. This is composed of a rotating shaft 17 that is a movable portion and a bearing housing 18 that is a fixed portion, and pressurized gas is ejected from the gas ejection surface 13 toward the rotating shaft 17, and the rotating shaft 17 is interposed via a bearing gap 15. And is supported rotatably. As shown in FIG. 4 (a), the radial projecting surface 16 a and the thrust projecting surface 16 b project independently from the bearing housing 18 at a portion spaced from the gas ejection surface 13, and the ambient pressure of the bearing gap 15 is respectively Surrounded by

  The projecting surface 16a is disposed to increase the radial direction damping characteristic of the rotating shaft 17, and the projecting surface 16b is disposed to increase the thrust direction damping characteristic of the rotating shaft 17. As shown in FIG. 4B, the protruding surface 16 a is arranged in four equal parts along the inner diameter of the bearing housing 18, but it does not have to be configured symmetrically with respect to the rotating shaft 17. Further, the shape and number of the projecting surfaces 16a and 16b are determined so as to obtain a perimeter corresponding to a frequency at which a necessary attenuation effect is obtained.

  In this embodiment, when a disturbance is applied to the rotating shaft 17, a pressure proportional to the relative speed in the radial direction of the rotating shaft 17 is generated, so that the gas interposed in the gap between the protruding surface 16a and the rotating shaft 17 functions as a damper. , Radial attenuation characteristics are improved. In the thrust direction, the same effect can be obtained by the protruding surface 16b, and the vibration of the rotating shaft 17 can be suppressed.

  FIG. 5 shows a fifth embodiment. Compressed air as pressurized gas is ejected from the gas ejection surface 23 of the bearing pad 22, and the projecting surface 26 is attached to the bearing pad 22 and is surrounded by the ambient pressure of the bearing gap at a portion separated from the gas ejection surface 23. It is. The bearing pad 22 is coupled to a movable part (not shown) by bolt fastening through a bearing pad mounting hole 29.

  For ease of mounting, as shown in FIG. 5 (a), the gas ejection surface 23 and the projecting surface 26 are the same plane, and the projecting surface 26 has a bearing pad mounting hole 29 as shown in FIG. 5 (b). It is provided in between. Since the gas ejection surface 23 and the projecting surface 26 are coplanar, fabrication is easy and a high damping effect can be obtained in a narrow space.

  When the attenuation effect in the present embodiment is obtained from the graph of FIG. 6, since the squeeze gap is 5 μm and there are four 8 × 8 mm projecting surfaces on the left and right, the maximum is 3.7 N / μm. That is, the squeeze gap is 40 μm, and the 50 × 50 mm protruding surface can increase the attenuation effect more than one. The protruding surface 26 is preferably made of a material having the same processing characteristics as the gas ejection surface 23.

DESCRIPTION OF SYMBOLS 1 Movable part 2, 22 Bearing pad 3, 13, 23 Gas ejection surface 4 Fixed part 5, 15 Bearing clearance 6, 16a, 16b, 26 Projection surface 17 Rotating shaft 18 Bearing housing

Claims (8)

In the gas bearing that ejects gas into the bearing gap between the movable part and the fixed part and supports the movable part by a gas film,
A bearing pad that has a gas ejection surface for ejecting gas in the bearing gap, is configured as a member different from the movable portion and the fixed portion, and is coupled to one of the movable portion and the fixed portion by bolt fastening. A bearing pad with a mounting hole ;
Projects before SL bearing gap, has a projecting surface which forms a 40μm following squeeze gap than 0.1μm between the other of said fixed portion and said movable portion opposing, spaced apart from the gas ejection face , a gas bearing, characterized in that it and a protruding portion that is attached to the bearing pads.   2. The gas bearing according to claim 1, wherein the same number of the protruding portions are arranged on both sides of the gas ejection surface. The gas bearing according to claim 1, wherein the projecting surface is divided into a plurality of lattice-shaped regions by grooves.   In the gas bearing that ejects gas into the bearing gap between the movable part and the fixed part and supports the movable part by a gas film,
  A bearing pad having a gas ejection surface for ejecting gas into the bearing gap;
  Projecting into the bearing gap and having a projecting surface that forms a squeeze gap of 0.1 μm or more and 40 μm or less between one of the fixed part and the movable part facing each other, the movable part and the fixed part A separate part, and a protruding portion attached to the other of the movable part and the fixed part apart from the gas ejection surface,
  The gas bearing according to claim 1, wherein the projecting surface is divided into a plurality of regions in a lattice shape by grooves shallower than a height of the projecting portion.   5. The gas bearing according to claim 4, wherein each region of the protruding surface has a circumference determined according to a natural frequency of a vibration system including the movable portion. The protruding surface is a gas bearing according to any one of claims 1 to 5, characterized in that it has a lubricating property. The gas bearing according to any one of claims 1 to 6 ,
A positioning stage supported by the gas bearing.   The gas bearing according to any one of claims 1 to 6,
  A bearing housing;
  A positioning device comprising: a rotating shaft disposed in the bearing housing and rotatably supported by the gas bearing.

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