JP3256315B2 - Pneumatic bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air dynamic pressure bearing for supporting a rotating shaft by utilizing the dynamic pressure of air, and more particularly to an improvement for increasing the load capacity and rigidity of the bearing.

[0002]

2. Description of the Related Art An air bearing in which a rotating shaft is supported in a non-contact manner by an air lubricating film is provided by a static pressure type in which a pressure applied to air is provided by a pressurizing machine such as a compressor, or by a shaft rotating without using a pressurizing machine. This is classified as a dynamic pressure type. Since the latter dynamic pressure type, that is, the air dynamic pressure bearing, does not require a pressurizing machine, it has the advantages that the device configuration can be simplified and the maintenance is easy as compared with the former static pressure type. Further, since a pressurizing machine is not required, there is an advantage that noise and vibration are not generated.

However, since the dynamic pressure type applies pressure to the air by rotation of the shaft, it has the drawbacks that the load capacity and rigidity are lower than those of the static pressure type, and that it is weak to fluctuating loads and impact loads. . For this reason, conventional air dynamic pressure bearings are used only for bearings with light loads and small load fluctuations, such as polygon mirrors for laser printers, and are required to have high rigidity and load capacity, for example, For the spindle and the like of the machine tool, a static pressure type had to be used.

In order to improve the load capacity and rigidity of the air dynamic pressure bearing, it is necessary to reduce the bearing clearance generated by the air lubricating film and increase the pressure applied to the air. Since shear friction heat is generated and the bearing material expands due to the shear friction heat, it is necessary to set the bearing clearance in consideration of the expansion.
There is a limit to designing bearing clearance small.

Conventionally, an air dynamic pressure bearing using ceramics as a bearing material has also been proposed for the purpose of suppressing fluctuations in bearing clearance due to thermal expansion. However, its load capacity and rigidity are still not sufficient. Also, it could not be used for bearings requiring high rigidity and load capacity.

[0006]

As described above, although the conventional pneumatic dynamic bearing has advantages as compared with the hydrostatic bearing, its use is remarkably limited due to its low rigidity and load capacity. This has hindered application to various bearing parts.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a pneumatic system which has a high rigidity and a high load capacity and is applicable to various bearings without being limited to the use. It is to provide a pressure bearing.

Another object of the present invention is to provide an air dynamic pressure bearing capable of suppressing fluctuations in bearing clearance due to heat generation of the bearing and ensuring high rigidity and load capacity.

[0009]

In order to achieve the above object, an air dynamic pressure bearing according to the present invention is fixed to a housing.
Clear the outer ring and the inner peripheral surface of this outer ring with the specified bearing clearance.
While maintaining the inner ring fixed to the rotating shaft
The radial dynamic pressure bearing and the axial direction of the inner ring of this radial dynamic pressure bearing
Fixed to the rotating shaft adjacent to both ends of the
Maintain the specified bearing clearance with the axial end face of the outer ring
A pair of opposed thrust dynamic pressure bearings,
The air, which is the working fluid, is directed to the center in the radial direction.
To form a pump-in type spiral groove to pressurize
Such a working fluid is used for thrust dynamic pressure bearing clearance.
From the bearing to the bearing clearance of the radial dynamic pressure bearing
On the other hand, the outer ring is sucked from outside the housing.
Pumped-in type thrust hydrodynamic bearing
A fluid supply passage for supplying to the outer peripheral edge of the spiral groove
It is formed along the axial direction, and the shaft of the radial dynamic pressure bearing
Supply the working fluid pressurized in the receiving clearance to the above fluid
The fluid discharge passage that discharges toward the passage
The radial dynamic pressure bearing and the
And the thrust hydrodynamic bearing pressurizes the above working fluid.
Radial hydrodynamic bearing and a pair of slurries
It is characterized in that it is configured to circulate between the strike dynamic pressure bearings .

[0010] In such technical means,
A pump-out type spiral groove is formed on the outer peripheral side of the pump-in type spiral groove of the thrust air dynamic pressure bearing, and the working fluid is supplied to the bearing at the boundary between the spiral grooves. Is preferred.

[0011]

The above technical means operates as follows. According to the air dynamic pressure bearing of the present invention, a pair of thrust air dynamic pressure bearings having a pump-in type spiral groove are provided on both sides of the radial air dynamic pressure bearing, and air as a working fluid is provided. Is pushed from the thrust air dynamic pressure bearing to the radial air dynamic pressure bearing, so that the amount of air circulation in the bearing increases, and the pressure applied to the air can be increased. As a result, the load capacity and rigidity of the air dynamic pressure bearing are improved.

Further, since the fluid passage for circulating the working fluid discharged from the radial pneumatic pressure bearing to the thrust pneumatic pressure bearing is provided, the working fluid having a high temperature due to shear friction heat may stay in the bearing. In addition, the cooling effect of the bearing is promoted. For this reason, the fluctuation of the bearing clearance due to the heat generated by the bearing can be suppressed and ignored, and the bearing clearance can be set smaller accordingly. As a result, the load capacity and rigidity of the air dynamic pressure bearing are further improved.

Further, since the cooling means for the working fluid is provided in the middle of the fluid passage, the working fluid from which the heat has been removed is always supplied to the bearing, so that the above-mentioned effect is more remarkably brought out.

Further, a pump-out type spiral groove is formed on the outer peripheral side of the pump-in type spiral groove of the thrust air dynamic pressure bearing, and a working fluid is supplied to the bearing at a boundary between the spiral grooves. As a result, a part of the working fluid supplied to the thrust air dynamic pressure bearing is pushed into the radial air dynamic pressure bearing by the pump-in type spiral groove, while the remaining working fluid is pumped by the pump-out type spiral groove. It is discharged to the outer periphery of the thrust air dynamic pressure bearing. For this reason, the air as the working fluid is not sucked into the thrust air dynamic pressure bearing from the outer peripheral side of the bearing, and the air circulating in the bearing is only supplied to the boundary of the spiral groove. Temperature control and cleaning of the air sucked into the bearing can be easily performed.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an air dynamic pressure bearing according to the present invention. FIG. 1 shows an embodiment of a spindle for a machine tool to which the present invention is applied. The spindle of this embodiment is of a built-in type in which a motor for driving the main shaft 1 is integrally incorporated, and includes a bearing portion 10 for supporting the rotation of the main shaft 1 and a motor portion 20 fixed to the bearing portion 10. ing.

First, the bearing portion 10 includes a main shaft 1 to which a tool or a workpiece (not shown) is fixed at a shaft end, and a radial pneumatic dynamic bearing for rotatably supporting the main shaft 1 with respect to a housing 2. (Hereinafter referred to as radial bearing) 3 and a pair of thrust air dynamic pressure bearings (hereinafter referred to as thrust bearings) 4 and 4.

The radial bearing 3 includes an inner ring 31 bonded and bonded to the main shaft 1 and an outer ring 32 shrink-fitted into the housing 2 while maintaining the inner ring 31 and a predetermined bearing clearance. On the peripheral surface of the inner ring 31, dynamic pressure generating grooves 33, 33 having a double herringbone pattern as shown in FIG. 2 are formed, the groove depth is 10 μm, and the number of grooves is 15 The groove angle β with respect to the main shaft rotation direction (the direction of the arrow A) is 30 °.
Accordingly, when the inner ring 31 rotates in the direction of the arrow A together with the main shaft 1, air as the working fluid flows from both ends in the axial direction of the inner ring 31 and the boundary between the herringbone-shaped grooves 33, 33 (arrow C position) to each herring. -It flows to the central part (arrow D position) of the bone-shaped groove 33, and a high dynamic pressure is generated at this position.

The pair of thrust bearings 4 and 4 are fitted and joined to the main shaft 1 so as to sandwich the inner ring 31 of the radial bearing 3, and the radial bearings 3 are held by holding plates 11 and 12 and set screws 13 and 14. The inner ring 31 is pressed against the inner ring 31. A dynamic pressure generating groove 41 having a spiral pattern is formed on the surface of each thrust bearing 4 on the radial bearing 3 side. FIG. 3 shows this dynamic pressure generating groove 4.
1 shows a pattern 1, in which a pump-in type spiral groove 42 is formed on the inner peripheral side and a pump-out type spiral groove 43 is formed on the outer peripheral side. Therefore, when the thrust bearing 4 rotates in the direction of the arrow B together with the main shaft 1, the pump-in type spiral groove 42 sucks the air as the working fluid in the inner circumferential direction, while the pump-out type spiral groove 43 draws the air in the outer circumferential direction. To discharge. Each spiral groove 42, 43 has a depth of 15 μm, 30 grooves,
The groove angle α with respect to the circumferential direction is 16 °. FIG.
R ₀ = 20 mm, R _m = 35 mm, R ₁ = 4 shown therein
2 mm, R ₂ = 44 mm, and R ₃ = 45 mm.

The outer ring 32 of the radial bearing 3 is formed such that its axial length is shorter than that of the inner ring 31 by 5 to 20 μm, so that a predetermined bearing is provided between the end face of the outer ring 32 and the thrust bearing 4. Clearance is maintained. When the thickness is 5 μm or less, the bearing clearance of each thrust bearing 4 is 2.5 μm or less, so that the undulation and flatness of the end surface of the outer ring 32 greatly affect the performance of the thrust bearing 4, and a large amount of air as a working fluid Shear friction heat is generated. When the thickness is 20 μm or more, the bearing clearance of each thrust bearing 4 becomes 10 μm or more, so that the load capacity and rigidity of the thrust bearing 4 decrease,
It is unsuitable as a spindle for machine work. Therefore, in this embodiment, this value is set to 10 μm.

The inner and outer rings 31, 32 and the thrust bearing 4 of the radial bearing are made of a ceramic material of an alumina sintered body, and the herringbone-shaped grooves 33 and the spiral grooves 41 are processed by shot blasting and abrasive liquid. It can be easily performed by ultrasonic processing, laser or the like in the inside. In the present embodiment, a resin mask was attached to the grooved surface of the inner ring 31 or the thrust bearing 4 and shot blasting was performed using Al ₂ O ₃ abrasive grains of 350 mesh. The appropriate groove depth is determined by the bearing clearance, but this time, the depth of the herringbone-shaped groove 33 of the inner ring 31 is set to 10 μm,
The depth of the spiral groove 41 of the thrust bearing 4 is 15 μm
And

A ring-shaped groove 34 is formed on the outer peripheral surface of the outer ring 32 of the radial bearing 3 along the circumferential direction, and the atmosphere in the ring-shaped groove 34 is formed by suction air formed in the housing 2. The port 21 communicates with the outside air. A filter 22 for removing dust and moisture from the outside air sucked into the housing 2 is attached to the intake port. Further, a fluid supply passage 35 that communicates and connects the ring-shaped groove 34 and the bearing clearances of the thrust bearings 4 and 4 passes through the outer race 32 in the axial direction, while the ring-shaped groove 34 and the bearing of the radial bearing 3 A fluid supply passage 36 that communicates with the clearance penetrates in the radial direction.
The opening of the fluid supply passage 35 on the thrust bearing 4 side faces the boundary between the pump-in type spiral groove 42 and the pump-out type spiral groove 43 formed in the thrust bearing 4. The opening of the fluid supply passage 36 on the radial bearing 3 side is opposed to the boundary between the doubly formed herringbone-shaped grooves 33, 33, that is, the position of the arrow C shown in FIG. These fluid supply passages 35,
Reference numerals 36 are formed at three places at equal intervals of 120 ° along the circumferential direction of the outer ring 32.

Further, the outer ring 32 is provided with the ring-shaped groove 3.
A fluid discharge passage 37 is formed for connecting the bearing 4 and the bearing clearance of the radial bearing 3 to each other. The fluid discharge passage 37 is formed at a position facing the formation position of the fluid supply passages 35 and 36 with the main shaft 1 interposed therebetween. The opening of the fluid discharge passage 37 on the radial bearing 3 side is opposed to the center of each herringbone-shaped groove 33, that is, the position of the arrow D shown in FIG.

Next, the motor section 20 will be described. Reference numeral 23 denotes a rotor coupled to the main shaft 1 via the holding plate 12, reference numeral 24 denotes a stator fixed to a motor housing 25, and the motor housing 25 The bearing 20 is fixed to the housing 2. A water jacket 26 is provided between the stator 24 and the motor housing 25, and the cooling water 27 prevents the stator 24 from overheating. Further, reference numeral 28 denotes a rotary encoder, which is configured to detect the rotation speed of the rotor 23, that is, the rotation speed of the main shaft 1. The motor unit 20 configured as described above is
Covered by

In FIG. 1, reference numeral 50 denotes the main shaft 1.
The reference numeral 51 denotes a magnet fixed to the holding plate 12 on the side, and the reference numeral 51 denotes a magnet 51 fixed to the housing 2 side, and is configured to float and support the main shaft in the axial direction by the repulsive force of these magnets. Thereby, even at the time of starting and stopping when the generation of the air dynamic pressure is insufficient, it is possible to prevent the thrust bearing 4 and the radial bearing 3 from making solid contact with each other.

When the rotor 23 of the motor section 20 rotates and the main shaft 1 connected thereto rotates in the spindle of the present embodiment configured as described above, the radial bearing 3 and the thrust bearing 4 are An air dynamic pressure is generated in the bearing clearance, and the rotation of the main shaft 1 is supported by the air lubrication film in a non-contact manner.

FIGS. 4 and 5 show the flow of air in the bearing 10 at this time. First, when the main shaft 1 rotates, the pump-in type spiral groove 42 of the thrust bearing 4 sucks air in the inner circumferential direction, while the pump-out type spiral groove 43 discharges air in the outer circumferential direction. The boundary between the grooves 42 and 43 has a negative pressure. Similarly, in the radial bearing 3, the boundary between the doubly formed herringbone-shaped grooves 33, 33 has a negative pressure. Therefore, as indicated by arrows in FIG. 4, the air outside the housing 2 is sucked into the link-shaped groove 34 through the intake port 21, passes through the fluid supply passages 35 and 36, and flows through the radial bearing 3 and the thrust bearing 4. Each is supplied to the bearing clearance.

At this time, since the bearing clearance of the thrust bearing 4 and the bearing clearance of the radial bearing 3 are connected to each other, the pump-in type spiral groove 42 of the thrust bearing 4 causes the air supplied to the thrust bearing 4 to be radial. It works to push it into the bearing 3. As a result, each bearing 3,
The amount of air circulating in the inside 4 increases, the pressure applied to the air can be increased, and the load capacity and rigidity of each of the bearings 3 and 4 improve.

At this time, since air is discharged from the outer periphery of the thrust bearing 4 by the action of the pump-out type spiral groove 43, the air is discharged from the outer periphery of the thrust bearing 4 to the bearing clearance of the thrust bearing 4. Does not enter at all. Therefore, the air supplied to the thrust bearing 4 and the radial bearing 3 is always sucked into the housing 2 through the filter 22 of the intake port 21, so that the air in the bearings 3 and 4 is always clean.

Next, considering the air pushed into the radial bearing 3 by the thrust bearing 4 or the air sucked into the radial bearing 3 by the fluid supply passage 36, these airs are formed in each herringbone shape formed on the inner race 31. The pressure is guided to the center of the grooves 33 (the position indicated by the arrow D in FIG. 2) and the pressure is increased. For this reason, as shown by an arrow in FIG. 5, the pressurized air is discharged to the ring-shaped groove 34 through the fluid discharge passage 37 formed in the outer ring 32. The air discharged to the ring-shaped groove 34 is supplied to the fluid supply passages 35 and 3.
6 again supplies the thrust bearing 4 and the radial bearing 3. That is, in the present embodiment, the thrust bearing 4
Only the amount of air discharged from the outer periphery of the housing to the outside of the housing is sucked into the housing 2 from the intake port 21, and the amount of air flowing into the radial bearing 3 is always circulating in the housing 2.

Therefore, the stagnation of the air heated to a high temperature due to the shear frictional heat in the bearings 3 and 4 can be prevented, and the thermal expansion of the inner ring 31 of the radial bearing 3 or the thrust bearing 4 can be suppressed. Further, since the air discharged from the radial bearing 3 contacts the housing 2 in the ring-shaped groove 34, the housing 2 serves to cool the hot air, and the air is supplied to the thrust bearing 4 before being re-supplied. The heat is removed. That is, in this embodiment, the housing 2 constitutes the cooling means of the present invention, whereby the thermal expansion of the inner race 31 or the thrust bearing 4 can be more effectively suppressed.

As a result, in the present embodiment, the bearing clearances of the radial bearing 3 and the thrust bearing 4 can be set smaller than before, so that the pressure applied to the air as the working fluid can be increased accordingly. Thus, the load capacity and rigidity of each of the bearings 3 and 4 can be increased.

The amount of air circulating in the housing is controlled by fluid supply passages 35 and 36 formed in the outer race 32 of the radial bearing 3.
And the diameter of the hole of the fluid discharge passage 37 can be freely adjusted, and this hole diameter is 0.2 to 2 mm. If it is less than 0.2 mm, it is difficult to process, and if it is more than 2 mm, excessive circulation occurs, and sufficient dynamic pressure cannot be generated in the air. Therefore, in this embodiment, these passages 35, 3
The hole diameter of 6, 37 was 0.5 mm.

The spindle of this embodiment has a main shaft 1
As the rotation speed of the main shaft 1 increases, the amount of air pushed into the radial bearing 3 from the thrust bearing 4 increases. Therefore, as the rotation speed of the main shaft 1 increases, the load capacity and rigidity improve.
Furthermore, if the rotation speed of the main shaft 1 increases, the circulation of air in the bearings 3 and 4 is promoted, so that the cooling effect of the bearings appears more remarkably. That is, the spindle of the present embodiment is more suitable for high-speed rotation.

In this embodiment, the air circulating in the housing 2 is cooled by allowing the housing 2 to cool naturally. However, the housing 2 is provided with a water jacket or the like to provide the fluid supply passages 35 and 36 and the fluid discharge passage. If the 37 is forcibly cooled, further effects can be obtained. Also,
In the present embodiment, the filter 22 is mounted on the inlet 21 to purify the air sucked into the housing 2. However, an air cleaner is provided outside the housing 2 so that the cleaner and the inlet 21 are connected by a hose. May be configured.

Table 1 below compares the performance and manufacturing cost of the spindle of this embodiment with the conventional spindle. In the table, the conventional product I is a spindle whose main shaft is supported by an aerostatic bearing with a bearing clearance set to 5 μm. The spindle speed is 8000 rpm.
I is a spindle bearing the main shaft with a ball bearing, and the main shaft rotation speed is 6800 rpm. Further, the spindle rotation speed in the present embodiment is 10,000 rpm. As is evident from the comparison results, the spindle of this example exhibited better results in terms of prevention of temperature rise, adaptability to high-speed rotation, and rigidity than the conventional product.

[0036]

[Table 1]

Table 2 below shows the load capacity and rigidity of the spindle of this embodiment and the spindle of the conventional product I. As is apparent from the comparison result, the spindle of this embodiment has a load capacity and a rigidity value which are remarkably improved as compared with the conventional product.

[0038]

[Table 2]

[0039]

As described above, according to the air dynamic pressure bearing of the present invention, the amount of air circulation in the bearing can be increased to increase the pressure applied to the air.
The load capacity and the rigidity can be increased by that much, and this air dynamic pressure bearing can be applied to various bearings without being limited to the intended use.

Further, since the cooling effect of the bearing is promoted and the fluctuation of the bearing clearance can be suppressed, the bearing clearance can be set smaller by that much, and also in this respect, the load capacity and rigidity of the air dynamic pressure bearing can be reduced. Can be further improved.

Further, since the working fluid from which heat has been removed is always supplied to the bearing, the above effect can be more remarkably obtained.

Furthermore, since the working fluid air is not sucked into the thrust air dynamic pressure bearing from the outer peripheral side of the bearing, the intake path of the working fluid into the bearing can be unified, and the working fluid is the working fluid. Air temperature control and cleaning can be easily performed.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a spindle to which an air dynamic bearing of the present invention is applied.

FIG. 2 is a view showing a pattern of a herringbone-shaped groove of the radial air dynamic pressure bearing according to the embodiment.

FIG. 3 is a diagram showing a spiral groove pattern of the thrust air dynamic pressure bearing according to the embodiment.

FIG. 4 is an explanatory diagram illustrating an intake path of a working fluid of a bearing unit according to the embodiment.

FIG. 5 is an explanatory diagram illustrating a working fluid discharge path of a bearing unit according to the embodiment.

[Explanation of symbols]

1 ... main shaft (rotary shaft), 3 ... radial air dynamic pressure bearing, 4 ...
Thrust air dynamic pressure bearings, 35, 36 ... fluid supply passages, 3
7 ... Fluid discharge passage, 42 ... Pump-in type spiral groove, 43 ... Pump-out type spiral groove

──────────────────────────────────────────────────続 き Continued from the front page (56) References JP-A-3-157513 (JP, A) JP-A-2-11918 (JP, A) JP-A 4-114020 (JP, U) JP-A 59-157 86412 (JP, U) (58) Fields studied (Int. Cl. ⁷ , DB name) F16C 17/00-17/26 F16C 33/00-33/28

Claims (2)

(57) [Claims] An outer race fixed to a housing and an outer race fixed to the outer race.
While maintaining a predetermined bearing clearance with the inner peripheral surface of the wheel,
Radial dynamic pressure bearing consisting of an inner ring fixed to a rolling shaft
And adjacent to both axial ends of the inner ring of this radial dynamic pressure bearing
And fixed to the rotating shaft and the axial direction of the outer ring
A pair of opposing ends is maintained with a predetermined bearing clearance.
And a thrust hydrodynamic bearing, the radial hydraulic fluid serving air to the thrust dynamic pressure bearing
Pump-in type spiral groove pressurizing toward the center of
To form such a working fluid into the thrust dynamic pressure bearing.
From rear lance to bearing clearance of radial dynamic pressure bearing
On the other hand, working fluid sucked from outside the housing is
Outer circumference of pump-in type spiral groove of last dynamic pressure bearing
Fluid supply passage to supply to the edge is formed along the axial direction
And within the bearing clearance of the radial dynamic pressure bearing
Discharging the pressurized working fluid toward the fluid supply passage
A fluid discharge passage formed along the radial direction that, the radial dynamic pressure bearing and thrust that with rotation of the rotary shaft
The above working fluid is radially
Dynamic pressure bearing and a pair of thrust dynamic pressures arranged at both ends
Characterized by circulating between bearings
Pneumatic bearing. 2. A pump-in type bearing for said thrust dynamic pressure bearing.
Pump-out type spiral on the outer peripheral side of the spiral groove
The working fluid passing through the fluid supply passage
Pump-in type spiral groove and pump-out type spy
To be supplied to the thrust hydrodynamic bearing at the boundary of the radial groove
The air dynamic pressure bearing according to claim 1, wherein: