JP3113750B2 - Hydrostatic gas bearing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic gas bearing used for precision machine tools and the like, and more particularly to a hydrostatic gas bearing suitable for high-speed rotation.

[0002]

2. Description of the Related Art In general, a static pressure gas bearing is widely used for a main shaft of a precision machine tool or the like because it has a small rotational torque, a high rotational accuracy, and requires almost no maintenance. The configuration of a conventional hydrostatic gas bearing is as follows.

(1) A cylindrical surface of a rotating shaft is opposed to a radial bearing pad of a bearing housing, and thrust plates are joined to both ends of the rotating shaft, and one surface of each thrust plate is opposed to a thrust bearing pad of the bearing housing. thing.

(2) The cylindrical surface of the rotating shaft faces the radial bearing pad of the bearing housing, and both surfaces of the thrust plate joined to one end of the rotating shaft face the thrust bearing pads of the bearing housing.

(3) A thrust plate is joined to the center of the rotating shaft, both surfaces of which are opposed to the thrust bearing pads of the bearing housing, and the cylindrical surfaces on both sides of the thrust plate are respectively opposed to the radial bearing pads of the bearing housing. thing.

In the prior art (1), since one side of each of the two thrust plates is opposed to the thrust bearing pad of the bearing housing, each thrust plate is caused to move outward or by centrifugal force due to the gas pressure in the bearing gap. It may be deformed inward, and the conventional example (2)
Since the rotating shaft is asymmetric in the axial direction, the rotating shaft may be inclined by its own weight. The conventional example (3) was developed to eliminate these drawbacks. In addition to the possibility that the thrust plate is deformed, the rotating body composed of the rotating shaft and the thrust plate is axially symmetric, Since there is no danger of the shaft being tilted, it is particularly suitable for high-speed rotation.

[0007]

However, according to the above-mentioned prior art, various obstacles occur during high-speed rotation.
That is, in any of the above conventional examples, the rotating shaft is composed of two or three parts, and when ceramic is used as the material of the rotating shaft, the strength is reduced due to the filling or tapping of the joint of each part, During high-speed rotation, there is a possibility of breakage due to stress concentration based on centrifugal force.

Conventionally, high-frequency motors and turbines have been used for high-speed rotation of the rotating shaft. In these cases,
Since the rotor of the motor and the turbine cascade are attached to the end face of the rotating shaft, the length of the rotating body including the drive system in the axial direction becomes longer, and as a result, the weight of the rotating body becomes larger and the resonance frequency is lower. Vibration easily occurs.

For example, in the case of a machine tool for machining a cylindrical workpiece with an outer diameter, a tool is mounted at one end of the spindle and the spindle is hollow to prevent time loss due to start and stop times of the spindle. It is desirable to feed the work material through the hollow part while constantly rotating, but if the length of the bearing part of the main shaft is long, the length of the chuck that holds the work material and passes through the hollow part of the main shaft is also long. Therefore, its rigidity is reduced, and good straightness cannot be obtained.

Further, in recent years, in order to reduce the machining tact, the spindle of the machine tool has been required to have a higher speed. However, when the conventional hydrostatic gas bearing is rotated at a high speed,
The rotating shaft expands due to heat generated by centrifugal force and shearing of the air film in the bearing gap, and as a result, the bearing gap decreases. Thus, the bearing gap decreases, the heat generation amount is more increased, Ru danger that the rotary shaft can not be smoothly rotated in contact with the bearing pads.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and has as its object to provide a hydrostatic gas bearing suitable for high-speed rotation.

[0012]

In order to achieve the above-mentioned object, a hydrostatic gas bearing according to the present invention comprises a rotating shaft which rotates in a non-contact manner.
And a bearing housing for supporting the bearing housing.
Cooling jacket with the bearing housing
Made of material with a larger coefficient of thermal expansion than the rotating shaft
Static bearing gas bearing, wherein the rotating shaft and the bearing
Detecting means for detecting a change in the size of the bearing gap during jing
The cooling jacket based on the output of the detecting means.
Control means for controlling the temperature and the flow rate of the refrigerant supplied to the tank
Is provided .

[0013]

[0014]

[0015]

[Action] by detecting a change in dimension of the shaft受間gap to adjust the temperature and flow rate of the cooling jacket, whereby by controlling the thermal expansion amount of the bearing housing, to maintain the size of the bearing gap to a predetermined value Can be.

[0016]

An embodiment of the present invention will be described with reference to the drawings.

[0017] Figure 1 is a schematic sectional view showing a first embodiment, the externally pressurized gas bearing E ₁ of the present embodiment includes a rotary shaft 1 which is provided such integrally with the main shaft of the machine tool, rotating it The rotating shaft 1 is a hollow body having a through hole 1a along the center axis thereof, and the hollow body is disposed between the pair of cylindrical portions 1b and 1c. Thrust plate portions 1d, which are integrally formed of a ceramic material. The bearing housing 2 has radial bearing pads 3a, 3b opposed to the cylindrical portions 1b, 1c of the rotating shaft 1, respectively.
Thrust bearing pads 4a opposed to each side D ₁ of the thrust plate portion 1d of the rotary shaft 1, having 4b. The cylindrical portions 2a and 2b of the bearing housing 2 holding the radial bearing pads 3a and 3b are respectively provided with cooling jackets 2c and 2c.
It is surrounded by 2d.

The air supply holes 5a and 5b for supplying pressurized gas to the radial bearing pads 3a and 3b are respectively opened in the central portion 2e of the bearing housing 2. Air supply holes 6a and 6b for supplying pressurized gas to the thrust bearing pads 4a and 4b are opened on the outer peripheral surface of the central portion 2e of the bearing housing 2.
The central portion 2e of the bearing housing 2 is provided with exhaust holes 5c and 5d respectively opening in bearing gaps A ₁ and B ₁ between the cylindrical portions 1b and 1c of the rotating shaft 1 and the bearing housing 2,
Exhaust hole 6 opening in turbine gap C ₁ between the outer peripheral surface of thrust plate portion 1 d of rotating shaft 1 and bearing housing 2
c.

Further, a turbine blade row 1e is formed on the outer peripheral surface of the thrust plate portion 1d of the rotary shaft 1, and a central portion 2e of the bearing housing 2 faces the turbine blade row 1e of the thrust plate portion 1d of the rotary shaft 1. And a turbine nozzle 7 for ejecting pressurized gas.

Each supply hole 5 is supplied from a pressurized gas supply source (not shown).
When the pressurized air is supplied to a, 5b, 6a, 6b, the rotating shaft 1 separates the cylindrical portions 1b, 1c of the rotating shaft 1 and the thrust plate from the radial bearing pads 3a, 3b and the thrust bearing pads 4a, 4b, respectively. is rotatably supported without the pressurized gas ejected toward both sides D ₁ of the portion 1d in contact with the bearing housing 2. Also,
Pressurized gas is supplied to the turbine nozzle 7 from the same pressurized gas supply source as described above or another pressurized air supply source,
When jetted toward the turbine cascade 1e, this causes the rotating shaft 1 to rotate at a high speed.

The bearing housing 2 is made of a material having a larger thermal expansion coefficient than the ceramic material of the rotating shaft 1. Both radial bearing pads 3a, 3b and both thrust bearing pads 4a, 4b are the same as the ceramic material. It is made of a material having a coefficient of thermal expansion of or higher. Therefore, when the rotating shaft 1 rotates at high speed, each bearing gap A
_1, the temperature of the rotary shaft 1 and the bearing housing 2 by the viscous friction of the B ₁ of the gas is increased, the bearing gap A _1, for better thermal expansion amount of the bearing housing 2 from the rotation shaft 1 is larger B _Although the size of ₁ increases, each cooling jacket 2
By providing a temperature difference between the rotating shaft 1 and the bearing housing 2 by adjusting the temperature of the refrigerant supplied to the refrigerant flow paths 2f and 2g of c and 2d, the dimensions of the bearing gaps A ₁ and B ₁ are set to predetermined values. Keep at the value.

The hydrostatic gas bearing according to the present embodiment is made of ceramic and integrally formed with a hollow rotary shaft having a thrust plate substantially at the center in the axial direction. There is no danger that the strength will decrease due to bolt holes, taps, burial, etc. that join the rotating shaft. Therefore, even if the rotating shaft is rotated at a high speed, there is no risk of generating vibrations or breaking due to stress concentration. In addition, a rotating shaft made of ceramic has a higher Young's modulus than a rotating shaft made of metal, and therefore, there is very little deformation or expansion due to centrifugal force during high-speed rotation.

Further, since the turbine blade cascade is formed on the outer peripheral surface of the thrust plate portion of the rotating shaft, the entire length of the rotating body including the rotating shaft and the drive system for rotating the rotating shaft can be shortened. In addition to making it easier to reduce the weight, it is also possible to shorten the length of the chuck that holds the work material when feeding the work material through the through hole of the rotating shaft, and to prevent the rigidity from lowering. it can.

FIG. 2 is an explanatory view for explaining a second embodiment. In this embodiment, a hydrostatic gas bearing E ₂ includes a rotating shaft 11 provided integrally with a main shaft of a machine tool and a rotating shaft 11. The bearing housing 12 includes a bearing housing 12 that supports the radial bearing pad 13a facing the cylindrical surface of the rotating shaft 11, and the outer peripheral surface of the bearing housing 12 is surrounded by a cooling jacket 12d. The bearing housing 12 has an air supply hole 15a for supplying a pressurized gas to the radial bearing pad 13a.
The air supply line 15b is connected to a pressurized gas supply source (not shown). The pressurized gas supplied from the pressurized gas supply source to the radial bearing pad 13a via the air supply line 15b is jetted toward the cylindrical surface of the rotating shaft 11, whereby the rotating shaft 11 is disengaged from the radial bearing pad 13a. It is supported by contact and rotated by drive means (not shown). The refrigerant passage 12f of the cooling jacket 12d is connected to a refrigerant supply line 12g and a refrigerant discharge line 12h, the refrigerant supply line 12g is connected to the discharge side of the circulator 20, and the refrigerant discharge line 12h is connected to a suction side.

The bearing housing 12 is provided with a rotating shaft 11.
Has a non-contact capacitive displacement sensor 18 which is a detecting means for detecting a change in the dimension T ₁ of the bearing gap A ₁ between the radial bearing pad 13a and, the displacement sensor 18 via the amplifier 18a It is connected to a controller 19 which is a control means for controlling the circulator 20.

Further, the bearing housing 12 includes the rotating shaft 11
Of are made of a material having a large coefficient of thermal expansion than the material, the temperature of the rotary shaft 11 and the bearing housing 12 during high speed rotation by the gas viscosity friction of the bearing gap A ₁ of the rotary shaft 11 increases, the rotation shaft 11 Since the thermal expansion of the bearing housing 12 is larger, the dimension T ₁ of the bearing gap A ₁ increases.

At the same time, since the rotating shaft 11 expands in the radial direction due to the centrifugal force acting on the rotating shaft 11, the amount of change of the dimension T ₁ of the bearing gap A ₁ detected by the displacement sensor 18 is From the increase in the dimension T ₁ of the bearing gap A ₁ due to the difference between the thermal expansion of the rotating shaft 11 and the rotating shaft 1.
The radial expansion due to the centrifugal force of No. 1 is subtracted.

As described above, when the rotation shaft 11 is rotated and the displacement sensor 18 detects a change in the dimension T ₁ of the bearing gap A ₁ , the controller 1 is operated based on the detected change.
9 is controlled, and the temperature and the flow rate of the refrigerant supplied from the circulator 20 to the refrigerant channel 12f of the cooling jacket 12d are adjusted. As a result, the bearing housing 12 is cooled to an appropriate temperature, and a change in the dimension T ₁ of the bearing gap A ₁ is prevented.

According to this embodiment, the change in the size of the bearing gap is detected by the displacement sensor, and the temperature and the flow rate of the refrigerant in the cooling jacket are adjusted based on the detected change. Therefore, there is no risk of seizure or conversely reducing bearing rigidity. In addition, since the bearing housing can be maintained at an appropriate temperature from the start, a running-in operation is unnecessary. Note that an optical or eddy current type non-contact type displacement sensor can be used instead of the non-contact capacitance type displacement sensor. Furthermore, instead of a displacement sensor that directly measures the change in the dimension of the bearing gap, the relationship between the temperature of the bearing housing and the change in the dimension of the bearing gap is measured in advance, and the measurement is performed by a temperature sensor attached to the side surface of the bearing housing. The change in the dimension of the bearing gap may be estimated by comparing the measured temperature of the bearing housing.

In addition, as shown in FIG. 3, a flow meter 28 is provided in an air supply line 25b for supplying a pressurized gas to an air supply hole 25a of a radial bearing pad 23a similar to the radial bearing pad 13a, and the output thereof is controlled. The circulator 30 may be controlled by estimating a change in the size of the bearing gap from a change in the flow rate of the pressurized gas supplied to the radial bearing pad 23a via the amplifier 28a to the controller 29. In addition, the rotating shaft 1
1, the bearing housing 12, and the cooling jacket 12d are the same as those in the apparatus shown in FIG.

[0031]

Since the present invention is configured as described above, the following effects can be obtained. A hydrostatic gas bearing suitable for high-speed rotation can be realized.

The first aspect of the present invention realizes a hydrostatic gas bearing which does not break or generate vibration due to an increase in centrifugal force during high-speed rotation.

The third aspect of the present invention realizes a hydrostatic gas bearing which does not cause seizure or decrease the bearing rigidity due to a change in the size of the bearing gap even when the rotational speed or the like changes. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment.

FIG. 2 is an explanatory diagram illustrating a second embodiment.

FIG. 3 is an explanatory diagram illustrating a modification of the device in FIG. 2;

[Explanation of symbols]

 1,11 Rotary shaft 1b, 1c Cylindrical part 1d Thrust plate part 1e Turbine cascade 2,12 Bearing housing 2c, 2d, 12d Cooling jacket 3a, 3b, 13a, 23a Radial bearing pad 4a, 4b Thrust bearing pad 5a, 5b, 15a, 25a Air supply hole 15b, 25b Air supply line 18 Displacement sensor 19, 29 Controller 20, 30 Circulator 28 Flow meter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-148102 (JP, A) JP-A 2-91219 (JP, U) JP-A 63-171726 (JP, U) JP-A 63-171726 11126 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F16C 32/00-32/06

Claims (4)

(57) [Claims] A shaft for rotatably supporting a rotating shaft in a non-contact manner.
A receiving housing and a cooling jar for cooling the bearing housing
A bearing housing, wherein the bearing housing is heated by the rotating shaft.
Hydrostatic gas axis made of a material with a high coefficient of expansion
A shaft between the rotating shaft and the bearing housing;
Detecting means for detecting a change in the size of the receiving gap, and the detecting means
Based on the output of the cooling
A hydrostatic gas bearing, wherein control means for controlling the temperature and flow rate of the medium is provided . 2. The method according to claim 1, wherein the detecting means is an optical type, a capacitive type or
Hydrostatic gas bearing according to claim 1, wherein the non-contact displacement sensor der Rukoto eddy current. 3. The method according to claim 2, wherein the detecting means detects a temperature change of the bearing housing.
And changes in the size of the bearing gap based on the temperature change
The hydrostatic gas bearing according to claim 1 , characterized in that: 4. A detecting means is provided on the bearing housing.
Changes in the flow rate of the flowing gas, and based on the
Externally pressurized gas bearing according to claim 1, characterized in that to estimate the change in the size of the gap.