JPH0730794B2 - Hydrostatic air bearing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrostatic air bearing used as a bearing for various precision equipment such as an ultra-precision processing machine, a measuring instrument, or a semiconductor manufacturing apparatus. .

[Prior Art] In general, this type of static pressure air bearing has an excellent advantage that its precision is extremely high as compared with a hydrostatic pressure bearing and other rolling bearings, but on the other hand, it has low rigidity. There is a drawback that. On the other hand, in recent high-precision measuring instruments, precision processing machines, and the like, static pressure air bearings having high rigidity are required in terms of precision and environment.

[Problems to be Solved by the Invention] Generally, in order to increase the rigidity of the hydrostatic air bearing, it is conceivable to use a large pocket, but unstable vibration may occur depending on the design and manufacturing method in that case. In particular,
In a hydrostatic air bearing, the magnitude of the spring constant and the magnitude of the damping coefficient are contradictory to each other. Therefore, if the spring constant is increased, the damping coefficient becomes small and unstable vibration is likely to occur. Conversely, in order to suppress the occurrence of unstable vibration, the spring constant must be sacrificed to some extent in order to increase the damping coefficient of the shaft. In order to deal with such a problem, a hydrostatic air bearing in which a magnetic fluid has been added to the inside of the bearing to increase the damping coefficient of the shaft has been conventionally used.
For example, it is disclosed in Japanese Utility Model Publication No. 2-27017.

However, in this conventional example, no deep insight has been made on the magnetic fluid or the container that accommodates it, and there is no description about an effective design method, so there is a possibility that the effect may not be obtained in some cases. is there. Further, since there is no hydrostatic air bearing designed in consideration of the damping coefficient, there is a problem in the convergence property and the resilience to the disturbance in the positioning of the table even when it is used in a measuring instrument or a machine tool.

Further, in a normal static pressure air bearing, fine self-vibration having an amplitude of about 0.01 μm is generated in the bearing itself, and when a drive system is further connected, a fine vibration having an amplitude of 0.1 μm or more is generated. These slight vibrations cause a decrease in precision in precision measurement and precision processing.

Therefore, in order to eliminate or reduce such micro vibration,
A method of adding a damper mechanism such as an oil damper mechanism or a friction mechanism to the outside of the bearing is adopted, but it is not possible to effectively remove the minute vibration that causes large equipment, and by such an external damper mechanism, rather There is also a case where it affects the motion accuracy and deteriorates.

The object of the present invention is to improve the damping characteristics of the entire bearing by adding a fluid damper to the hydrostatic air bearing in order to improve such a problem, and to reduce the damping coefficient and unstable vibration due to high rigidity. Another object of the present invention is to provide a static pressure air bearing which prevents the occurrence of the above and further allows an optimum damping coefficient to be arbitrarily set.

A further object of the present invention is to mount a hydrostatic air bearing that can eliminate or reduce self-vibration generated in the bearing itself or microvibration due to disturbance of the drive system to obtain more stable bearing performance.

[Means for Solving the Problems] In order to achieve the above-mentioned object, in a hydrostatic air bearing according to the present invention, in a sliding hydrostatic air bearing having a fixed portion and a movable portion, the fixed portion and the movable portion are movable. One of the parts has a recess provided in the direction of gravity, and a protrusion provided on the other so as to fit in the recess with a minute gap, and has a viscosity interposed in the minute gap. A damping damper mechanism made of an uncompressed fluid and having a variable damping coefficient is provided, and the damping coefficient of the damping damper mechanism is the size of the minute gap, the size of the facing area between the recess and the protrusion, and the uncompressed value. It is characterized in that it is set according to at least one of the viscosity of the fluid.

[Operation] The static pressure air bearing having the above-described configuration is designed to have The damping coefficient is set to an appropriate value, and the fluid damper suppresses minute self-vibration generated in the bearing itself and minute vibration caused by disturbance.

[Examples] The present invention will be described in detail based on the illustrated examples.

FIG. 1 is a sectional view showing an embodiment in which the present invention is applied to an airway static pressure air bearing, and FIG. 2 is a plan view thereof. One of the members forming the static pressure air bearing is a guide member 1, the other movable member is a slider 2, and a suitable bearing gap g is provided between them by compressed air injected from an air nozzle 3 of the slider 2. Is held. A recess 4 extending in the moving direction is formed in the guide member 1 at a position where the bearing function is not hindered, and an incompressible fluid A such as water, silicone oil, or other hydraulic fluid is supplied into the recess 4. Has been done. Further, the slider 2 is integrally formed with a protrusion 5 which is fitted into the recess 4 via a minute gap which is a damper gap, and a non-contact member interposed in the damper gap between the recess 4 and the protrusion 5. The compressed fluid A constitutes a damper mechanism.

In the case of this embodiment, as shown in FIG. 3, the damper gap D1 between the bottom surface of the concave portion 4 and the tip surface of the projecting body 5 corresponds to the movement of the slider 2 in the Y direction, and X The damper gap D2 between the side surface of the concave portion 4 and the side surface of the projecting body 5 corresponds to the movement in the direction, and each constitutes a damper mechanism. In this case, the damping characteristic, that is, the change in the damping coefficient, is determined by the area of the opposing surfaces forming the damper gaps D1 and D2 of the projecting body 5, the size of the damper gaps D1 and D2, and the viscosity of the incompressible fluid A. .

FIG. 4 and FIG. 5 show a second embodiment in which the recess 4 has a substantially V-shaped cross-section, and the projection 5 fitted therein has a V-shape corresponding to the recess 4. Shows. In the case of this embodiment, as shown in FIG. 6, movement of the slider 2 as a movable member in the X and Y directions can be accommodated by the damper gap D3 in the oblique direction.

FIG. 7 shows an experimental apparatus for adjusting the damping characteristic in the vertical direction when applied to the formed thrust bearing, and FIG. 8 shows an example of the nozzle arrangement of the thrust bearing portion 11. In this case, one member constituting the static pressure air bearing is the thrust bearing portion 11, and the other member is the thrust plate 12, and the air nozzle arranged on the upper surface of the thrust bearing portion 11.
A bearing gap g is held between the two by compressed air from 13. Further, the thrust bearing portion 11 is provided with a concave portion 14 for containing the non-compressed fluid A on the upper surface thereof, and the thrust plate 12 is fitted with the concave portion 14 via a proper damper gap D.
15 is integrally formed, and a load 16 is arranged on the thrust plate 12.

In this experimental device, the thrust bearing 11 has an outer diameter of 100 mm.
φ, the inner diameter is 54 mmφ, and the air nozzle 13
There are 16 in total, 8 in each of the inner and outer circles. In addition, the thrust plate 12 and the load placed on it
The total load of 16 is 14 Kgw. Further, as the non-compressed fluid A, silicone oil having a viscosity of 0.0002 Kgf / cm.S is used.

In this device, the bottom of the recess 14 is movable in the vertical direction,
The size of the damper gap D can be changed.
In order to investigate the damping characteristics in the vertical direction using this device, as shown in FIG. 9, an impact force is applied from above and the damper gap D is further changed to see how the thrust plate 12 moves. When used for measurement, the results shown in FIG. 10 were obtained. In FIG. 10, a curved line a shown by a solid line shows the damping characteristic of only the hydrostatic air bearing without a fluid damper, and a broken line b shows a damper gap D when the damper gap D is set to 100 μm. When set to 50 μm, the two-dot chain line d shows the respective damping characteristics when the damper gap D is set to 10 μm.

As shown by the experimental results, the damping characteristics of the entire bearing can be set arbitrarily by displacing the damper gap D between the concave portion 14 and the projecting body 15 by using, for example, a piezoelectric element. Of course, the damping characteristic of the bearing can also be set by changing the viscosity of the non-compressed fluid A present in the damper gap D or the area of the surface facing the damper.

Although the above is an example by experiment, the damping characteristics of a hydrostatic air bearing having such a fluid damper mechanism can be obtained by calculation, and the appropriate damping coefficient required for general precision processing machines and measuring instruments can be obtained. It is possible to arbitrarily design the static pressure air bearing with. Further, in addition to the action as the damping characteristic described above, the viscosity of the non-compressed fluid A also acts as the damping in the movement direction of the bearing movable member, so that this function can be effectively used.

Further, in the case of a thrust bearing, as shown in FIGS. 11 and 12, the recess 14 may be an annular groove, and at least three protrusions 15 fitted into the recess 14 may be provided for balance. .

When the hydrostatic air bearing is actually installed as an element part in various types of precision processing machines and measuring machines, etc., an appropriate damping coefficient for disturbances such as load fluctuations and environmental changes received by the actual machine or hydrostatic air bearings Is possible. For example, by controlling the size of the damper gap described above by a minute displacement mechanism such as a piezoelectric element, an appropriate damping coefficient can be actively obtained.

In addition, in this embodiment, in addition to the thrust bearing and the airway bearing,
It can be applied to all static pressure air bearings such as air spindles.

[Advantages of the Invention] As described above, in the hydrostatic air bearing according to the present invention, by adding the fluid damper mechanism in the bearing, the generation of the unstable vibration and the damping coefficient accompanying the high rigidity of the hydrostatic air bearing are achieved. Can be prevented. Further, since a damping mechanism can be added, an appropriate damping coefficient can be set without sacrificing rigidity depending on the application of the static pressure air bearing. Furthermore, by mechanically changing the damper gap in response to dynamic fluctuations in the bearing, a control mechanism that obtains an appropriate damping coefficient is possible.

Further, since the fluid damper acts to suppress the minute self-vibration generated in the bearing itself and the minute vibration due to the disturbance of the drive system, it is possible to reduce the influence of these minute vibrations in the precision measurement and the precision machining. It is possible to obtain stable performance and accuracy.

[Brief description of drawings]

The drawings show an embodiment of a hydrostatic air bearing according to the present invention.
FIG. 3 is a sectional view of the first embodiment, FIG. 2 is its plan view, and FIG.
FIG. 4 is an explanatory view of its operation, FIG. 4 is a sectional view of the second embodiment,
FIG. 5 is a plan view, FIG. 6 is an explanatory view of operation, FIG. 7 is a sectional view of a third embodiment applied to a thrust bearing, FIG. 8 is a plan view of a thrust bearing portion, FIG. 9, and FIG. FIG. 11 is a graph of experimental values, FIG. 11 is a sectional view of the fourth embodiment, and FIG. 12 is a sectional view taken along the line BB of FIG. Reference numeral 1 is a guide member, 2 is a slider, 3 is an air nozzle,
Reference numeral 4 is a recess, 5 is a protrusion, 11 is a thrust bearing portion, 12 is a thrust plate, 13 is an air nozzle, 14 is a recess, 15 is a protrusion, and 16 is a load.

Claims (4)

[Claims] 1. A sliding type static pressure air bearing having a fixed portion and a movable portion, wherein a concave portion provided in one of the fixed portion and the movable portion in the direction of gravity and a minute gap in the concave portion. A damping damper mechanism having a variable damping coefficient, which comprises a protrusion provided on the other side so as to be fitted together and an incompressible fluid having viscosity interposed in the minute gap, and the damping coefficient of the damping damper mechanism is provided. Is set according to at least one of the size of the minute gap, the size of the facing area of the recess and the protrusion, and the viscosity of the incompressible fluid. 2. The hydrostatic air bearing according to claim 1, wherein damping coefficient control means for actively controlling a damping coefficient is added to the damping damper mechanism. 3. The hydrostatic air bearing according to claim 2, wherein the damping coefficient control means is a minute displacement mechanism for controlling the size of the minute gap. 4. The hydrostatic air bearing according to claim 3, wherein the minute displacement mechanism is a piezoelectric element.