JP5645560B2 - Static pressure gas bearing - Google Patents

Description

  The present invention relates to a static pressure gas bearing that improves the rotational accuracy of a rotating body represented by a main shaft of a precision processing machine.

  High rotational accuracy is required for a rotating body typified by a main spindle of a precision processing machine, and a static pressure gas bearing that rotatably supports the rotating body in a non-contact manner is generally used. In the static pressure gas bearing, the flow rate is adjusted so that the flow rate of the gas ejected from the bearing portion is uniform when released into the atmosphere.

  FIG. 3 shows a conventional example of a static pressure gas bearing. The rotating body 107 has a thrust portion 115, one porous body 108 disposed at a position facing one plane of the thrust section 115, and the other porous body disposed at a position facing the other plane. 109 supports the rotating body 107 in the direction of the rotation axis. FIG. 3 shows a case where one plane and the other plane of the thrust portion 115 are parallel to a virtual plane that intersects the rotation axis perpendicularly. However, the plane of one porous body 108 facing the thrust portion 115 of the rotating body 107 is not parallel to a virtual plane that intersects the rotation axis perpendicularly. In this case, even if the rotating body 107 rotates as shown by the arrow and the phase with one porous body 108 changes to change from the state shown in FIG. 3A to the state shown in FIG. The bearing gap 110 with the thrust portion 115 of the rotating body 107 viewed from the porous body 108 side does not change.

  FIG. 4 shows another conventional example of a static pressure gas bearing. FIG. 4 shows a case where the plane facing the thrust portion 115 of one porous body 108 is parallel to a virtual plane perpendicular to the rotation axis. However, one plane of the thrust portion 115 is not parallel to a virtual plane that intersects the rotation axis perpendicularly. In this case, even if the rotating body 107 rotates and the phase with one porous body 108 changes as shown by the arrow, and the state changes from FIG. 4A to FIG. The bearing gap 110 with the porous body 108 viewed from the side does not change. If one of the planes of the thrust part 115 and one porous body 108 and the other porous body 109 is parallel to the virtual plane, the gas film of the one porous body 108 and the other porous body 109 The pressure distribution is uniform and no shaft shake occurs.

  However, since the machining accuracy is limited, the machined surface always has a shape error. As a method for correcting the deviation caused by the shape error, a method based on flow rate adjustment is known. For example, in Patent Document 1, when a deviation occurs in the coaxiality of the fixed bell holder shaft and the movable bell holder shaft, the flow rate of the gas ejected from the static pressure gas bearing portion formed of the porous body is adjusted. Thus, a method for improving the matching accuracy is disclosed.

JP 2003-39291 A

  In the case of trying to achieve nanometer-order rotational accuracy as required for the spindle of ultra-precision processing machines, simply by improving the coaxiality by adjusting the gas flow rate as in the conventional example above. Is insufficient.

  In the static pressure gas bearing shown in FIG. 5, the surface of the porous body 108 facing the plane of the thrust portion 115 and the one surface of the thrust portion 115 are both virtual planes perpendicular to the rotation axis. Not parallel. Therefore, when the rotating body 107 rotates and the phase between one porous body 108 and the other porous body 109 changes, the bearing gap 110a shown in FIG. 5A changes to 110b shown in FIG. 5B. It will change. As a result, the pressure distribution of the gas film that is ejected from one porous body 108 and the other porous body 109 and formed in the bearing gap changes, and the rotating body tilts, causing shaft shake and lowering the rotational accuracy. Resulting in.

  Since it is difficult to machine the surface of the rotating body facing the porous body parallel to the virtual plane perpendicular to the rotation axis without a shape error, the shape usually has a shape error from the ideal shape. ing. In the conventional example, the bearing gap including the shape error of both the thrust part and the porous body is measured to adjust the flow rate, and when the phase of the thrust part with respect to the porous body changes, the value of the bearing gap varies. Will do.

  If the rotational accuracy is on the order of several hundred nanometers, which has been required in the past, the variation in the bearing gap due to the shape error of the thrust part and porous body will be the effect of averaging the gas film that is ejected from the porous body and formed in the bearing gap Because of this, it was canceled to the extent that it would not be a problem. However, when a nanometer order is required as the rotation accuracy, a slight change in the bearing clearance is a factor that degrades the rotation accuracy.

  An object of this invention is to provide the static pressure gas bearing which can achieve the high rotation precision of a nanometer order.

In order to achieve the above object, the static pressure gas bearing of the present invention provides a surface of a porous body provided with a thrust load of a rotating shaft of a rotating body having a thrust portion protruding in a bowl shape so as to face the thrust portion. in the externally pressurized gas bearing for supporting the gas blown from the opening holes in said multi Anashitsutai, the from one region of the surface of the porous body, exchange perpendicular to the axis of rotation of said rotary member Li Kui When the length of the perpendicular when the perpendicular is lowered to the virtual plane facing the surface of the porous body is used as a reference distance, the perpendicular when the perpendicular is lowered from the area different from the certain area to the virtual plane. The opening amount of the surface of the porous body in the region where the length of the perpendicular is longer than the reference distance is larger than the opening amount of the surface of the porous body in the certain region, and from a region different from the certain region Of the perpendicular when the perpendicular is dropped on the virtual plane Saga, the opening amount of the surface of the porous body region shorter than the reference distance, characterized in that it is configured to be less than the opening amount of the surface of the porous body of the certain region.

  This is equivalent to the fact that the surface of the porous body is parallel to a virtual plane perpendicular to the rotation axis of the rotating body, and even if the rotating body rotates and the phase between the thrust part and the porous body changes, the bearing The pressure distribution of the gas film formed in the gap is uniform.

  For this reason, it becomes possible to always support the rotating body so as to be freely rotatable with a constant force, the occurrence of the shaft shake is eliminated, and the rotation accuracy is greatly improved.

The static pressure gas bearing by one Embodiment of this invention is shown, (a) is a schematic cross section, (b) is a schematic top view of the porous body holding | maintenance part provided in the housing. It is a graph which shows the relationship between a bearing clearance and a support pressure. It is a schematic cross section which shows the case where the phase of a rotary body and a bearing part changes. It is a schematic cross section which shows the case where the phase of a rotary body and a bearing part changes. It is a schematic cross section which shows the case where the phase of a rotary body and a bearing part changes.

  An embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1A, the static pressure gas bearing according to the present embodiment has a thrust portion 19 in which the rotating body 24 protrudes in a bowl shape in the radial direction of the rotating shaft 20. One surface and the other surface of the thrust portion 19 are parallel to a virtual plane 21 that intersects the rotation axis 20 perpendicularly. In the housing 12, one porous body 13 is disposed via a porous body holding portion at a portion facing one surface of the thrust portion 19. The porous body holding part of the housing part 12 includes a gas supply channel 22 and an adhesive surface 23 to the porous body. One porous body 13 and the other porous body 14 are bonded and fixed to the housing 12 by the bonding surface 23. Further, pressurized gas is supplied from the housing portion 12 to the porous bodies 13 and 14 through the gas supply path 22. The pressurized gas discharged from the porous bodies 13 and 14 is exhausted to the surroundings through the exhaust holes 25 formed in the housing 12.

  As shown in FIG. 1B, the porous body holding portion of the housing portion 12 is composed of a concentric gas supply path 22 communicating with one pressurized gas supply hole 18a and the other adhesive surface 23. ing. The porous body is composed of many pores that cause a gas flow to the side. Gas can be ejected from the entire bearing surface of the porous body without supplying pressurized gas from the entire surface of the porous body. .

  The rotating body 24 has a thrust portion 19 protruding like a bowl in the radial direction of the rotating shaft 20. One porous body 13 is disposed at a position facing one plane of the thrust portion 19, and the other The other porous body 14 is disposed at a position facing the plane.

  The features of the present invention will be described. Conventionally, in a bearing using a porous body, the flow rate of the gas that permeates and is ejected through the porous body is adjusted to be uniform on the surface of the porous body that becomes the bearing surface. However, the bearing gap fluctuates due to a planar shape error between the surface of the porous body and the plane of the thrust portion, and shaft runout of the rotating body occurs.

  In the present invention, the surface of the porous body is measured by a measuring instrument such as a flatness measuring instrument, and the distance (planar shape error) between the virtual plane 21 and the porous body that intersect perpendicularly to the rotation axis 20 is determined. According to this distance (planar shape error), the pressure for supporting the thrust load of the rotating body can be made constant by changing the flow rate of the gas ejected from the porous bodies 13 and 14. . The occurrence of shaft runout occurs because the pressure supporting the thrust load of the rotating body changes during one rotation. Therefore, the flow rate of the gas that is permeated and ejected from the regions of the porous bodies 13 and 14 that are at least the same radial distance from the rotation axis 20 is the virtual plane 21 that intersects the rotation axis 20 perpendicularly and each porous body. It is necessary to make them different according to the distance from 13 and 14 (planar shape error). The flow rate of the ejected gas is changed depending on, for example, the amount of sealing applied to the porous body surface. In this specification, the term “sealing” refers to an action of spraying lacquer or the like on the surface of the porous body to block the pores on the surface of the porous body. Moreover, the amount of sealing means the amount which blocked the hole of the porous body. Thereby, it becomes possible to adjust the number of the holes opened on the surface of the porous body.

  Next, a method for changing the flow rate of the gas ejected from the porous bodies 13 and 14 will be described.

  First, the surfaces of the porous bodies 13 and 14 are measured with a measuring instrument such as a flatness measuring instrument. For each measurement point set on the surface of each porous body 13, 14, the distance from the virtual plane 21 that intersects the rotation axis 20 perpendicularly is obtained. The distance from the virtual plane 21 is determined for each measurement point located on the same circumference having the same radial distance from the rotation axis 20. On the same circumference is a surface whose distance from the rotating shaft 20 is within a certain range. The certain range is, for example, a range of several mm to several cm, and within this range, the effects of the present invention can be sufficiently obtained.

  As is generally done in the past, the flow rate of the gas ejected from the bearing at the time of release to the atmosphere is adjusted to be uniform at the measurement points located on the same circumference of the porous bodies 13 and 14. To do. Then, the pressure for supporting the rotating body 24 is not uniform in the bearing gap between the porous bodies 13 and 14 and the thrust portion 19, and the shaft of the rotating body 24 is generated. Therefore, the flow rate of the gas ejected from each porous body 13, 14 so as to compensate for the non-uniformity of the distance from the virtual plane 21 perpendicular to the rotation axis 20 on the surface of each porous body 13, 14. Depending on the amount of sealing applied to the surface of the porous body.

  For example, a certain region on the same circumference of the porous bodies 13 and 14 is set as the reference region. A distance from the virtual plane 21 of the reference area is set as a reference distance. If another region on the same circumference is the first region, if the distance from the virtual plane 21 of the first region is longer than the reference distance, the flow rate of the gas ejected from the first region is The amount of sealing applied to the surface of the porous body is adjusted so as to increase more than the flow rate ejected from the reference region. In other words, the opening amount of the holes in the first region is made larger than that in the reference region. If another region on the same circumference is the second region, if the distance from the virtual plane 21 of the second region is shorter than the reference distance, the flow rate of the gas ejected from the second region is The sealing amount is adjusted so that the flow rate is smaller than the flow rate ejected from the reference region. That is, the opening amount of the hole in the second region is made smaller than that in the reference region. The distance between the region and the virtual plane can be obtained from, for example, an average value of the lengths of the perpendiculars when a perpendicular is dropped from each point of the region to the virtual plane. The accuracy is improved by setting this region as narrow as possible. It goes without saying that the most excellent effect is obtained by measuring each point (each hole) on the surface of the porous body.

  As described above, by adjusting the flow rate, the pressure for supporting the rotating body 24 of the bearing is always uniform even during rotation. That is, the support point of the rotating body 24 is a point on a plane that intersects the rotating shaft 20 perpendicularly. For this reason, this is equivalent to the surface of each porous body 13, 14 being parallel to a virtual plane 21 perpendicular to the rotation axis 20 of the rotator 24, and in the circumferential direction of each porous body 13, 14. A uniform support pressure can be obtained.

  The flow rate adjustment amount is determined as follows. There is a correlation as shown in FIG. 2 between the bearing clearance and the support pressure of the hydrostatic gas bearing. This represents the relationship between the bearing gap and the support pressure when the flow rate at the time of air release ejected from a certain point on the surface of the porous body is constant. This relationship is obtained by solving the Reynolds equation representing the gas flow in the bearing gap by the difference method, and obtaining the relationship between the bearing gap and the pressure in the bearing gap.

  In FIG. 2, attention is paid to a point m on the curve w7. It is assumed that the bearing clearance has changed to a point n on the curve w7. At point n, the bearing pressure is increased because the bearing gap is widened. When this change occurs during the rotation, the support balance of the rotating body 24 is lost, and shaft shake occurs. A curve w8 is a graph showing the relationship between the bearing clearance and the support pressure when the flow rate during release to the atmosphere is higher than w7. In order to increase the support pressure at the point n, the amount of sealing applied to the surface of the porous body is decreased to increase the flow rate at the time of air release, and the point o on the curve w8, which is the same bearing gap, It is possible to obtain a support pressure equivalent to m at the bearing gap at point n. The characteristics of such a static pressure gas bearing are obtained by simulation, and a flow rate value at the time of opening to the atmosphere at which a support pressure equivalent to the point m can be obtained is calculated.

As a specific example, the flow rate adjustment amount is calculated from the flow characteristics actually used and the bearing clearance. The bearing characteristic curve w7 in FIG. 2 assumes that the flow rate when released to the atmosphere is 57 sccm / cm ² and the point m on w7 is when the bearing clearance is 5 μm. When the distance from the virtual plane perpendicular to the rotation axis increases due to an error in the surface shape of one of the porous bodies 13, and the bearing gap becomes 6 μm, the support pressure decreases and becomes a point n on w7. End up. If this is the case, the support balance of the rotating body 24 will be lost and shaft wobbling will occur. Therefore, it is necessary to obtain a support pressure equivalent to the point m on w7 which is the case of the bearing clearance of 5 μm even at the point n of the bearing clearance of 6 μm. There is. Therefore, the flow rate is increased by loosening the sealing amount applied to the surface of one porous body 13 and increasing the opening amount of the holes. In this specific example, by increasing the flow rate to 98 sccm / cm ² , the bearing characteristic curve w8 passing through the point o indicating the support pressure equivalent to that when the bearing gap is 5 μm is obtained even when the bearing gap is 6 μm. Will be shown. By adjusting the flow rate in this way, a supporting pressure equivalent to the point m on w7 which is the case of the bearing gap 5 μm can be obtained even at the point n in the case of the bearing gap 6 μm.

  This flow rate adjustment is performed in each region on the same circumference of one porous body 13. Each region on the same circumference may be a region divided in the circumferential direction and does not need to be equally divided. Also, it is better that the number of area divisions is larger.

  Further, in the static pressure gas bearing in the present embodiment, the support pressure does not have to be uniform in the radial direction, but by adjusting the flow rate based on a plurality of circumferential planar shapes at a plurality of radii. Thus, a more uniform support pressure in the circumferential direction can be obtained.

DESCRIPTION OF SYMBOLS 12 Housing part 13 One porous body 14 The other porous body 19 Thrust part 20 Rotating shaft 21 Virtual plane

Claims (4)

A hydrostatic gas bearing that supports a thrust load of a rotating shaft of a rotating body having a thrust portion protruding in a bowl shape by a gas ejected from a hole opening in a surface of a porous body provided to face the thrust portion. In
The multi-Anashitsutai is,
From a region of the surface of the porous body, a reference length of said vertical lines when a perpendicular line is dropped on the surface facing the imaginary plane perpendicular to exchange Li Kui the porous body with respect to the rotational axis of the rotary body When distance
The amount of opening of the surface of the porous body in the region where the length of the perpendicular when the perpendicular is lowered from the region different from the certain region to the virtual plane is longer than the reference distance, More than the opening amount of the surface of the porous body,
The amount of opening of the surface of the porous body in the region where the length of the perpendicular when the perpendicular is lowered from the region different from the certain region to the virtual plane is shorter than the reference distance is set in the region. A hydrostatic gas bearing characterized by being configured to be smaller than the opening amount of the surface of the porous body .   2. The hydrostatic gas bearing according to claim 1, wherein an opening amount of the surface of the porous body is adjusted by closing a hole on the surface of the porous body.   The static pressure gas bearing according to claim 2, wherein the hole is blocked by a lacquer.   A housing having a porous body holding portion for holding the porous body at a portion facing the thrust portion;
  4. The hydrostatic gas bearing according to claim 1, wherein the porous body holding portion has a concentric gas supply path for supplying pressurized gas to the porous body. 5.

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