JPH017849Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrodynamic gas bearing device capable of pivotally supporting a shaft body and a bearing in a non-contact manner.

Conventionally, in a hydrodynamic gas bearing device, a plurality of grooves are carved in a herringbone shape, that is, inclined at a certain angle with respect to the axial direction, on the outer peripheral surface of a cylindrical shaft body that is supported by a cylindrical bearing. A herringbone groove bearing device is used. The above-mentioned herringbone groove has a groove depth of several tens of micrometers or less and is inclined at a certain angle with respect to the axis, so normal machining cannot be applied, and groove machining is suitable for special machining such as chemical corrosion machining. Relying on. However, the chemical corrosion processing described above requires complicated steps such as pattern drawing, film creation, resist coating, exposure, etching, etc.
Not only is the production efficiency extremely low, but since the grooves are formed by chemical corrosion, the cross-sectional shape of the grooves is limited to a rectangular shape, which is undesirable from the viewpoint of generating dynamic pressure. Moreover, since the groove is inclined at a certain angle with respect to the axial direction, the direction of rotation of the shaft body is fixed, and if the shaft rotates in the opposite direction all the time, there is a risk of serious damage.

The present invention was made in consideration of the above circumstances, and by providing a plurality of grooves equally spaced in the outer peripheral surface of the shaft body, the cross-sectional shape of which has a symmetrical circular arc shape and which is parallel to the axial direction. An object of the present invention is to provide a hydrodynamic gas bearing device that is easy to machine and has improved performance as a bearing.

Hereinafter, the present invention will be described in detail based on embodiments with reference to the drawings.

The hydrodynamic gas bearing device shown in FIG. 1 is a type of so-called journal bearing, and includes a cylindrical bearing 1 and a cylindrical shaft body 2 with a slightly smaller diameter than the bearing 1, which is supported by the cylindrical bearing 1. It is composed of. As shown in FIG. 2, a plurality of linear grooves 3 parallel to the central axis of the shaft 2 are equally distributed on the outer peripheral surface of the shaft 2. These grooves 3 are manufactured by milling using a ball end mill, for example, and the cross-sectional shape perpendicular to the central axis of each groove 3 is an arc, as shown in Figure 3, and its maximum depth is , several tens of μm to several hundred μm
is within the range of Thus, the cross-sectional shape of each groove 3 perpendicular to the central axis is symmetrical.

Therefore, when the shaft body 2 is rotated at a high speed of, for example, 10,000 rpm or higher in this hydrodynamic gas bearing device, a dynamic pressure as shown by the dynamic pressure curve 4 in FIG. 3 is generated as the shaft rotates. The shaft body 2 is supported by the bearing 1 in a completely non-contact manner. The above-mentioned dynamic pressure is generated by a combination of the vortices of the air caught in the grooves 3 and the wedge action of each groove 3 on the inner circumferential surface of the bearing 1. Therefore, the spindle using the hydrodynamic gas bearing device of this embodiment can stably rotate at tens of thousands of rpm with high precision. Incidentally, FIG. 4 shows the rotational stability of the hydrodynamic gas bearing device of this embodiment and the conventional herringbone groove bearing device. In this figure, Λ is a dimensionless number called a compressibility number and is given by the following equation.

Λ=6μω/Pa(R/Cr) ² ...where, μ is the gas viscosity coefficient, ω is the rotational angular velocity,
Pa is the atmospheric pressure, R is the radius of the shaft, and Cr is the radial clearance of the bearing. On the other hand, is called the stability limit value and is given by the following equation.

= ω (MCr/PaLD) _1/2 … However, L is the length of the shaft, D is the shaft diameter, and R
twice, M is the mass of the shaft. In FIG. 5, the groove depth is given by the following equation.

=δ/Cr... In other words, when =1, it indicates that the radial clearance and the groove depth are equal. In FIG. 4, the stable/unstable regions of the hydrodynamic gas bearing device of this embodiment are 1, 2, and 3, and the stable/unstable regions of the herringbone groove bearing device where the groove inflow angle β is 25° are 1.35.
Regions of instability are shown. However, in this case,
Eccentricity ε=0.5L/D=1. In this figure, in the unstable region, whirling occurs and an unstable phenomenon occurs, and in the other stable region, whirling does not occur and highly accurate rotation can be obtained. Thus, as shown in FIG. 4, the hydrodynamic gas bearing device of this embodiment can maintain rotational stability even in a large Λ region of Λ=50 or more, compared to a herringbone groove bearing device. . In other words, the hydrodynamic gas bearing device of this embodiment can be used stably without seizure even at higher speeds or when the bearing clearance is smaller than the herringbone groove bearing device. Therefore, a wide range of design conditions can be adopted, and as a result, the versatility of the bearing device is greatly improved, which is an exceptional effect.
Furthermore, as mentioned above, since the grooves 3 are formed linearly and parallel to the central axis of the shaft body 2, it is possible to form the cross-sectional shape of the grooves 3 into an arc by machining, which is different from the conventional method. Compared to groove formation by special machining, groove processing can be performed more efficiently and with high precision. Therefore, by forming the cross section of the grooves 3 in an arcuate shape, the dynamic pressure is increased and the performance as a gas bearing is improved compared to a square shape such as a conventional herringbone groove. Furthermore, since the grooves 3 have a symmetrical arc cross-sectional shape and are formed in a straight line and parallel to the central axis, the bearing performance is the same for both forward and reverse rotations. can be obtained.

In the above embodiment, the cross-sectional shape of each groove 3 perpendicular to the axial direction is a circular arc, but is not limited to this, and may be an elliptical arc as long as the cross-sectional shape perpendicular to the axial direction is symmetrical.

As described above, the hydrodynamic gas bearing device of the present invention is
The outer circumferential surface of the shaft body has a symmetrical arc cross-sectional shape and multiple grooves parallel to the axis are equally distributed, making it possible to apply normal machining to groove formation. Compared to conventional herringbone groove bearing devices, grooves can be formed quickly, with high precision, and at low cost. Furthermore, the bearing characteristics have been improved and the same bearing performance can be obtained for both forward and reverse rotations, resulting in easier bearing design conditions than herringbone groove bearing devices. This has the extraordinary effect of improving the versatility of the device.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view perpendicular to the axial direction of a hydrodynamic gas bearing device according to an embodiment of the present invention, FIG. 2 is a perspective view of the hydrodynamic gas bearing device shown in FIG. 1, and FIG. FIG. 4 is a sectional view of a main part of a hydrodynamic gas bearing device, and FIG. 4 is a graph showing a stability curve of the bearing. 1...Bearing, 2...Shaft body, 3...Groove.

Claims (1)

[Scope of utility model registration request] The shaft has a cylindrical shaft and a bearing that pivotally supports the shaft, and the shaft has a cross-sectional shape perpendicular to the axial direction that is symmetrical and parallel to the axial direction. A dynamic pressure gas bearing device characterized in that a plurality of dynamic pressure generating grooves are formed at equal intervals.