JP2724349B2 - Hydrostatic air bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hydrostatic air bearing used for, for example, an ultra-precision processing machine or a precision measuring instrument.

2. Description of the Related Art Conventionally, as a static pressure air bearing of this type, a self-contained restricting method and an orifice restricting method with a pocket are mainly known as restricting methods.

FIGS. 8 and 9 show models of the self-contained restrictor and the orifice restrictor with pocket, respectively. FIGS. 10 and 11 show the positions where the air flow is restricted, respectively.

In the drawings, 1 is a shaft, 2 is a bearing main body, and G is a shaft gap therebetween. In the self-contained throttle system, as shown in FIG. 8, air at a supply pressure Ps is directly injected from the nozzle 3 into the shaft gap G, and the position A where this air flow is throttled is as shown in FIG. This is near the exit of the nozzle 3 of G. On the other hand, in the orifice throttle system with a pocket, as shown in FIG. 9, a pocket 5 having a considerable depth is formed following the orifice 4, and as shown in FIG. It remains within the range of the nozzle 4.

[Problems to be Solved by the Invention] Generally, in this type of hydrostatic air bearing, due to the presence of the throttle, a secondary pressure is generated in the downstream portion of the throttle with respect to the supply pressure Ps. As a result, a spring constant, generally called rigidity, occurs in the bearing.

In the case of a self-contained throttle, it is common to reduce the nozzle diameter, reduce the shaft gap G, and reduce the throttle area in order to increase the spring constant. However, when the throttle area is extremely reduced, Since the original function of the bearing is lost, there is a limit in reducing the shaft clearance G, and there is a disadvantage that the spring constant cannot be increased too much.

On the other hand, the orifice diaphragm with pocket is pocket 5
Has the advantage that the spring constant can be set higher than the self-contained throttle, but in the relationship between the shaft gap G and the spring constant, the size Cr of the shaft gap G at which the spring constant is maximized In the vicinity, the damping coefficient extremely decreases and sometimes becomes a negative value, so that the bearing body is likely to be in an unstable state such as causing self-excited vibration.

12 and 13 show how the pressure distribution in the shaft gap G changes with respect to the shaft gap variation in the self-generated throttle and the orifice throttle with pocket, respectively, where Pa is the atmospheric pressure, Ps is the supply pressure, and Po is the pocket pressure. 5 shows the pressure, and the change in pressure indicated by hatching is the spring constant. Since the orifice throttle with a pocket has the pocket 5, the amount of pressure change is large with respect to the fluctuation of the shaft gap G, and a higher spring constant can be set than in the case of the self-generated throttle. However, in the relationship between the shaft clearance G and the spring constant, the size of the shaft clearance G at which the spring constant is maximized
In the vicinity of Cr, the attenuation coefficient is extremely reduced or negative, so
The bearing is in an unstable state in which self-excited vibration easily occurs. Therefore, in order to secure a positive damping coefficient and stabilize the shaft, it is necessary to set a shaft clearance at the expense of the spring constant. There is no problem.

An object of the present invention is to improve such problems.
An object of the present invention is to provide a hydrostatic air bearing having a high spring constant and good stability by making the depth of the pocket at the nozzle tip shallow enough to form a self-constricted state in the pocket.

Means for Solving the Problems In order to achieve the object of the present invention, in a hydrostatic air bearing according to the present invention, there is provided a hydrostatic air bearing having a throttle type having an end pocket at a nozzle tip. diameter d, characterized by ^{πd 2/4> πd (H} + Cr) and that passed a H / Cr = 0.5 to 1.5 between the depth H and the axial gap size Cr of the pocket.

[Operation] In the hydrostatic air bearing having the above-described configuration, a self-contained throttle is formed in the pocket by making the pocket depth almost as small as the shaft gap, and the effective cross-sectional area of the throttle is reduced by the nozzle. Since the diameter is smaller than the effective cross-sectional area, the maximum spring constant value can be obtained with a smaller shaft clearance than the orifice throttle with a pocket even if the nozzle diameter is the same. Further, since the pocket depth is shallow, a decrease in the attenuation coefficient is prevented.

Embodiment The present invention will be described in detail based on an embodiment shown in FIGS.

FIG. 1 shows a composite throttle type hydrostatic air bearing according to the present invention, in which 11 is a shaft, 12 is a bearing body, 13 is a nozzle, and the depth of a pocket 14 following the nozzle 13 is equal to that of a self-formed throttle. It is shallow enough to work. Here, when the ratio of the pocket depth H to the size Cr of the shaft gap G is in the range of H / Cr = 0.5 to 1.5, it was experimentally confirmed that a maximum spring constant value and a high damping coefficient were obtained. Have been.

FIGS. 2 (a) and 2 (b) are specific bearing dimensions and nozzle position (arrow N) dimensions of the radial bearing for the data shown in FIGS. 3 to 6, for example. FIG. 7 is a dimensional diagram of a self-generated throttle, an orifice throttle with a pocket, and a composite throttle. The data shown here is for the case where the supply pressure is 5 kgf / cm ² G.

In FIG. 3, the horizontal axis is H / Cr, the vertical axis is the spring constant for the optimum clearance of the bearing, that is, the maximum spring constant value, and the vertical axis is the data showing the relationship with the spring constant value for the optimum clearance of the bearing. Similarly, FIG. 4 shows data in which the horizontal axis is H / Cr and the vertical axis is the dimensionless damping coefficient for the optimum clearance of the bearing.

From these two data, it is clear that the maximum spring constant is obtained when H / Cr is in the range of 0.5 to 1.5, and that the value of the damping coefficient at the maximum spring constant value is high.

As shown in FIG. 1, when a shallow depth of the pocket 14 to about the same extent as the magnitude Cr axis gap G, i.e. the relationship between the nozzle diameter d and H and ^{Cr, πd 2/4> πd} (H + Cr) when the holds, i.e. than the cross-sectional area [pi] d ^2/4 of the nozzle 13 having a diameter d that serves as an orifice aperture, circumferential area [pi] d of virtual cylindrical body consisting of the diameter d and height which functions as a self-formed aperture (H + Cr) When (H + Cr) is small, the position C where the air flow is restricted is formed in both the pocket 14 and the shaft gap G. An aperture format having this function is called a composite aperture.

FIG. 5 shows the relationship between the size Cr of the shaft gap G and the spring constant in the composite throttle type hydrostatic air bearing according to the present invention, when the supply pressure is 5 kgf / cm ² G and the conventional self-contained throttle. And F, a composite orifice according to the present invention, J represents a conventional self-contained restrictor, and P represents an orifice restrictor with a pocket.

In the case of the composite aperture F, the effective area of the aperture is small,
Orifice throttle P with conventional pocket even if nozzle diameter is the same
The maximum value of the spring constant can be obtained with a smaller shaft clearance, and the maximum spring constant value is larger than that of the orifice throttle P with a pocket. Further, since the maximum spring constant value can be obtained with a narrow gap, the amount of air used can be significantly reduced as compared with the conventional orifice throttle P with a pocket.

FIG. 6 similarly shows the relationship between the size Cr of the shaft gap G and the dimensionless damping coefficient in comparison with the conventional method.
Represents an unstable region of the orifice diaphragm P with a pocket. As can be seen from FIG. 6, the composite diaphragm F of the present invention is used.
Since the depth of the pocket 14 is shallow, a decrease in the damping coefficient can be prevented, and the damping coefficient does not decrease as much as the orifice restrictor P with the pocket even at the size Cr of the shaft gap G showing the maximum spring constant value. The bearing body can maintain stability.

The composite throttle F can be applied to a hydrostatic air table having the same function as a hydrostatic air bearing, and is also applied to an optimum control of an active hydrostatic air bearing for controlling a pocket depth of a nozzle. be able to.

[Effects of the Invention] As described above, the hydrostatic air bearing according to the present invention has a larger spring constant with a smaller shaft clearance than an orifice throttle with a pocket by having the function of a self-generated throttle in the pocket. As a result, the shaft clearance can be reduced, and the amount of consumed air can be reduced. Further, since the size of the shaft gap having the maximum spring constant is greatly deviated from the unstable region, it is possible to sufficiently maintain the stability even if the shaft gap greatly changes.

[Brief description of the drawings]

1 to 7 show an embodiment of a hydrostatic air bearing according to the present invention. FIG. 1 is a diagram showing the principle of a composite throttle, FIG.
(B) is a dimensional diagram of the radial bearing used in the experiment, FIG. 3 is a characteristic diagram of a change in the maximum spring constant, FIG. 4 is a characteristic diagram of a change in the dimensionless damping coefficient at the maximum spring constant value, and FIG. FIG. 6 is a characteristic diagram showing the relationship between the spring constant and the shaft clearance, FIG. 6 is a characteristic diagram showing the relationship between the dimensionless damping function and the shaft clearance, and FIG. 7 is a dimensional diagram of the nozzle. Fig. 8 shows a conventional static pressure air bearing throttle system, Fig. 8 is a configuration diagram of a self-generated throttle, Fig. 9 is a configuration diagram of an orifice throttle with a pocket, Fig. 10 is an explanatory diagram of a self-generated throttle, Fig. 11 Is the illustration of the orifice diaphragm with pocket, twelfth
FIG. 13 is a graph showing a pressure distribution state of a self-contained throttle, and FIG. Reference numeral 11 denotes a shaft, 12 denotes a bearing body, 13 denotes an orifice, 14 denotes a pocket, and G denotes a shaft clearance.

Claims (1)

(57) [Claims] 1. A static pressure air bearing having a throttle type having an end pocket at a nozzle tip, wherein πd ² is defined between a diameter d of the nozzle, a depth H of the pocket, and a size Cr of a shaft clearance.
/ 4> πd (H + Cr) and H / Cr = 0.5 to 1.5.