JPH0663537B2 - Air bearing with dynamic pressure groove - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a groove on the surface of a shaft, and by rotating the shaft,
An air bearing that generates compressed air on the load pressure receiving surface by viscously surrounding air, and brings the bearing and shaft into a non-contact state by the lubricating action and dynamic pressure effect of this compressed air,
In particular, it relates to a vertical type air bearing with a dynamic pressure groove.

[Conventional technology]

(1) FIGS. 4 and 5 show the principle of this type of air bearing, which is a diagram quoted from the document: World Encyclopedia 8 (Heibonsha), and FIG. 4 is a sectional view of the air bearing, FIG. 5 is a perspective sectional view showing the flow of air in the bearing. In FIG. 5, a slide bearing in which a part of the shaft 102 (referred to as a journal) 104 is supported by the inner surface of the bearing 106 is a lubricating oil having an appropriate viscosity in order to reduce resistance and wear due to friction between the journal 104 and the bearing 106. Is applied to the contact surface so that the bearing 106 supports the journal 104 through the oil film. In this case, the air bearing uses the viscosity of air 108 instead of oil, and it was first used in the gyro by Pibbins of the United States in 1922. The structure is shown in FIG.
Through a plurality of air holes 110 drilled in the journal 104
When air of appropriate pressure is blown on the contact surface with (when using a plain bearing at high speed, the air pressure (kg / cm ² ) is about 7 to 11 times the axial load (kg / cm ² )) With the rotation of the bearing, it flows spirally as shown in FIG. 5 and flows out into the bearing. The size and position of the air hole 110 are determined in relation to the distribution of bearing pressure due to the axial load.

What has been described above is a radial bearing that supports a shaft load perpendicular to the center line 112 of the shaft.
The thrust bearing that supports the axial load parallel to the
This can be achieved by blowing air 108 from the end surface of the shaft 102 between the end surface of the shaft 108 and the stepped collar portion of the shaft 102. The above-mentioned one is a horizontal type, but it can be realized by a vertical type, and the one explained above is a combination of commonly used bearing fixing and shaft rotation. But,
On the contrary, it is possible to realize a combination of bearing rotation by fixing the shaft. This type of air bearing requires an air supply mechanism such as a compressor and piping, and is called a static pressure air bearing.

(2) The air supply mechanism was required in the above (1) static pressure air bearing, but by providing a spiral groove called a dynamic pressure groove in either one of the shaft and the bearing, rotation of the shaft or the bearing is improved. There are radial and thrust air bearings that are supported by lubrication by the accompanying air flow. This is called a dynamic pressure grooved air bearing, and it does not require an air supply mechanism, and both bearing fixing and shaft fixing can be realized.

In each of the air bearings (1) and (2), since air is used as a lubricant, replenishment is easy everywhere, and unlike oil, there is no fear of polluting the surroundings, and there is no leakage. It is ideal for bearings of machines that dislike oil, such as food, chemicals and medical equipment, because the viscosity of air is 1/1 of that of lubricating oil.
Since it is 1000, bearing friction is 1/1000 and it can be rotated lightly. In addition to the above advantages, since the compressed air can be generated by the dynamic pressure grooved air bearing by itself, the air supply mechanism such as the compressor and piping, which is indispensable for the static pressure air bearing of (1) above, is unnecessary. The size of the entire device can be reduced. Therefore, the dynamic pressure grooved air bearing is used as a bearing for a gyro, a rotor of a magnetic drum, a polygon mirror drive motor for a laser scanner, etc., which is small and requires high speed rotation.

[Problems to be Solved by the Invention]

However, not only the air bearing with dynamic pressure groove but also the air bearing has a structure that is supported by compressible air, so that vibration is likely to occur at the time of rotation. You cannot expect decay. Vibration due to unbalance of rotating parts such as shafts and bearings
In principle, it is possible to remove the unbalance by detecting and correcting the unbalance with high accuracy using a commercially available balancing tester. However, vibration due to whirling instability (hereinafter referred to as whirl) causes rotation. Since it is different from the vibration caused by the unbalance of parts,
It cannot be removed even by modification. Since the object of the present invention is to provide an air bearing that suppresses this whirl, in the following, first, a case of a combination of bearing fixing and shaft rotation, which is commonly used for this whirl, will be described. In the case where the shaft is fixed in the opposite direction and the bearing is rotated, the idea is the same, and therefore the description is omitted in this case.

The whirl is the radius of the eccentricity e while the center of the rotating shaft does not match the center of the bearing and the rotating shaft rotates at the angular velocity ω, and the bearing center is at the angular velocity Ω in the same direction as the rotating direction of the rotating shaft. It is a phenomenon that revolves around. This orbital motion is caused by the air film turning around the axis, and the average speed of the air film at this time is approximately ω / 2. Therefore, the relationship of ω = 2Ω is established between ω and Ω. is doing. In particular, when Ω coincides with the natural frequency ω ₁ of the rotating shaft, it becomes self-excited vibration and the vibration due to the whirl suddenly increases, and the vibration amplitude increases until the shaft and the bearing come into contact and seize.

The whirl generation condition and its stability condition have been clarified by various mathematical methods, and from the analysis results, the smaller the radial load is, the more easily the whirl occurs.
Especially in the case of vertical installation, there is no radial load due to the self-weight of the shaft, and it has been clarified that the rotational speed becomes unstable from zero.

Therefore, when the air bearing is used as the vertical axis, it has been conventionally practiced to eliminate the instability by applying a radial load as one of the measures for suppressing the whirl, for example, the centrifugal separation shown in the sectional view of FIG. There are hydrostatic air bearings used in the machine. This is because the rotor 114 has a bearing 116 as shown in FIG.
It is arranged so that its axis coincides with the vertical direction,
It is configured as a static pressure air bearing that introduces compressed air between its contact surfaces to lubricate and support the rotor 114, and a gauge pressure of 0.7 to 3.5 kgf / cm ² from one of the radial bearing surfaces via the air supply pipe 118 to the nozzles 120 and 122. This compressed air is blown onto the rotor 114 to apply a radial load from the left to the right in FIG. 6, and the radial load suppresses the generation of whirl.

However, in order to adopt the method of applying a radial load to the shaft by blowing air in this way, an air supply mechanism such as a compressor and piping is required for this, so it is necessary to reduce the size of the entire device. Not only is it impossible, but it is economically problematic because of the equipment cost and operating cost for that purpose.

INDUSTRIAL APPLICABILITY The present invention uses a compressed air generated by a dynamic pressure effect of a spiral dynamic pressure groove to generate a radial load, and a whirl generated in a vertical type dynamic pressure grooved air bearing is newly added to a compressor and a pipe. It is an object of the present invention to provide an air bearing that can be suppressed without providing an air supply mechanism such as.

[Means for Solving the Problems]

In order to solve the above-mentioned object, the present invention provides a shaft having at least one pair of Yamaba grooves formed of a pair of grooves having spiral directions opposite to each other on the radial load pressure receiving surface, and a bearing for supporting the shaft. A bearing having a trapezoidal cut surface in a cutting plane including the center line of the shaft, the bearing being cut at two end surfaces thereof in two planes intersecting each other in an oblique direction with respect to the center line of the shaft. The radial load pressure receiving surface is lubricated by the compressed air generated by mixing the air with its viscosity to support the shaft in a non-contact state with the bearing, and the radial load pressure receiving surface is distributed asymmetrically with respect to the center of the shaft. Radial load generated by air pressure suppresses whirling instability of the shaft.

[Action]

The present invention, as shown in the perspective view of FIG. 2, includes a shaft 4 having a Yamaba groove 2 formed of a pair of grooves whose spiral directions are opposite to each other on a radial load pressure receiving surface, and a bearing 6 supporting the shaft 4. A dynamic pressure grooved air bearing comprising:
6a, 6b are cut along two planes that intersect with each other in the oblique direction with respect to the center line of the shaft 4, and the cutting plane of the bearing 6 at the AA cutting plane in FIG. As shown in the figure, it has a trapezoidal shape.

2 and 3, when the shaft 4 is rotated in the direction of arrow 20, the rotation of the shaft 4 causes the surrounding air to be lubricated with the compressed air generated by the surrounding air as dynamic pressure grooves. Then, the shaft 4 is supported by the bearing 6 in a non-contact manner.

FIG. 3 is a cross-sectional view showing the principle of suppressing the above whirl, and illustrates the pressure distribution of the compressed air generated on the bearing surface. The bearing 6 has a trapezoidal cross section and the bearing length is L on the left.
l, right is Lr, and Ll> Lr, so the maximum air pressure is on the left
When Pl and Pr on the right side are set, Pl> Pr. Therefore, if the pressure distribution is integrated over the entire circumference of the shaft, a radial load (F) indicated by the arrow 22 is generated, and as described above, this radial direction The load can suppress the generation of whirl.

〔Example〕

FIG. 1 is a perspective sectional view showing an embodiment of the present invention, which is based on the structure and operation described in FIGS. 2 and 3 above. In FIG. 1, a shaft 4 provided with at least one pair of Yamaba grooves 2 having a pair of grooves having spiral directions opposite to each other on the radial load pressure receiving surface, and a bearing 6 for supporting the shaft 4 and both end surfaces thereof A bearing 6 having a trapezoidal cutting surface in the cutting plane including the center line of the shaft 4 and 6a, 6b cut in two planes intersecting with each other in a diagonal direction with respect to the center line of the shaft 4; An air bearing with a dynamic pressure groove having a dynamic pressure groove 2 is configured. A central portion of the shaft 4 serves as a rotor 8 of the motor, and a bearing 6 is embedded with a stator 10 of the motor. A driven body 12 such as a hexagonal polygonal mirror is fixed to the upper end of the shaft 4. Further, in order to support the thrust load due to the own weight of the rotating body composed of the shaft 4, the rotor 8 and the driven body 12, the magnets 14 and 16 are
A magnetic bearing 18 of a passive type is provided. When the stator 10 is energized, the rotor 8 generates a rotational force,
The entire rotating body rotates in the direction of arrow 20.

The radial load pressure receiving surfaces of the shaft 4 and the bearing 6 are lubricated by the compressed air generated by the rotation of the shaft 4 causing the surrounding air to be mixed in with the viscosity of the surrounding air, so that the shaft 4 is not supported by the bearing 6. Bearing in contact. Further, both end surfaces 6a, 6 of the bearing 6 are
Since b is cut obliquely, radial load 22 (F) is generated on the radial load pressure receiving surface due to air pressure asymmetrically distributed with respect to the center of the shaft, and as described above, this radial load is applied. 22 (F) suppresses whirl which is the whirling instability of the shaft 4.

The present invention constitutes an air bearing that uses the groove 2 as a dynamic pressure groove as described above.

〔The invention's effect〕

According to the present invention, the radial load surface has spiral directions opposite to each other.
An air bearing with a dynamic pressure groove was constructed by combining a shaft provided with one or two pairs of Yamaba grooves formed of a pair of grooves and a bearing whose both end surfaces were cut obliquely. The whirl of the whirling instability of the shaft caused by the radial load asymmetrically generated with respect to the center, especially when used as the vertical axis for vertical installation,
It is possible to provide an air bearing with a dynamic pressure groove that can be suppressed without adding a special air supply mechanism.

[Brief description of drawings]

FIG. 1 is a perspective sectional view showing an embodiment of the present invention, FIGS. 2 and 3 are views for explaining the operation of the present invention, FIG. 2 is a perspective view, and FIG. 3 is A-A in FIG. Sectional views taken along the cut planes, FIGS. 4 and 5, are drawings showing the principle of this type of air bearing, which is cited from the World Encyclopedia 8 (Heibonsha), and FIG. 4 is a sectional view of the air bearing. FIG. 5 is a perspective sectional view showing the flow of air in the bearing, and FIG. 6 is a sectional view of a hydrostatic air bearing showing a countermeasure for suppressing whirl used in a centrifugal separator. 2 …… Yamaba groove, 4 …… Shaft, 6 …… Bearing, 12 …… Driven object, 18 …… Magnetic bearing, 22 …… Radial load (F),
102 …… Shaft, 104 …… Journal, 106, 116 …… Bearing, 110
…… Air holes, 114 …… Rotor.

Claims (1)

[Claims] Claim: What is claimed is: 1. A shaft having at least one pair of Yamaba grooves formed by a pair of grooves having spiral directions opposite to each other on the radial load pressure receiving surface, and a bearing for supporting the shaft, the both end surfaces of which are the center of the shaft. A bearing having a trapezoidal cut surface in the cutting plane including the center line of the shaft, the bearing being cut in two planes intersecting with each other in an oblique direction with respect to the line, and surrounding air is viscously entrained by the rotation of the shaft. The radial load pressure receiving surface is lubricated by the generated compressed air to support the shaft in a non-contact state with the bearing, and the radial load generated by the air pressure distributed asymmetrically on the radial load pressure receiving surface with respect to the center of the shaft An air bearing with a dynamic pressure groove characterized by suppressing the whirling instability of the shaft.