JPH09257038A - Spindle head for machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support the main spindle of a machine tool with sufficient bearing rigidity and to perform high speed rotation with high-precision and a high-load. SOLUTION: A spindle head 10 for a machine tool comprises a main spindle 30 rotationally driven by a built-in motor 40; air bearings 50 and 60 supporting the main spindle 30 radially and axially thereof; and a housing 20 to contain the air bearing 50 and 60. In this case, a plurality of the air bearings 50 and 60 are formed at bearing bushes 25, 26, and 27, and the air bearings 50 and 60 form a self-throttle type air hydrostatic bearing using air nozzles 51 and 61. Exhaust grooves 52 and 62 are formed between the air nozzles 51 and 61 and by exhausting the section, a restoration force during displacement of the axis of the main spindle 30, and bearing rigidity is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle head for machine tools, and can be used for NC machine tools for performing high-speed feed cutting such as high-precision end milling.

[0002]

BACKGROUND ART Conventionally, N has been required for high precision machining of metal parts and the like.
C (numerical control) type machine tools are used. In such a machine tool, a tool is attached to the tip of a spindle supported by a spindle head, and the spindle head is moved relative to the workpiece while rotating the spindle or the tool to move the workpiece. We are cutting.

(Regarding bearing of main spindle) In a machine tool having such a rotary main spindle, it is required to rotate the main spindle at a high speed while maintaining high accuracy under a considerable load. For example, when performing end milling, if the spindle is rotated at high speed at tens of thousands of revolutions per minute while maintaining high accuracy,
It has been confirmed that high-efficiency machining at cutting feed rates of up to several meters per minute is possible. Therefore, it is important to support the spindle in the spindle head of machine tools.
This bearing portion is required to satisfy the conditions of high load, high accuracy and high speed rotation.

(Rolling bearing and oil bearing) Conventionally, as a bearing structure for supporting the main shaft, a rolling bearing such as a ball bearing, an oil bearing for supporting the main shaft by an oil film, an air bearing for supporting the main shaft by air pressure, etc. have been used. Has been done. However, rolling bearings and oil bearings have not been able to sufficiently satisfy the conditions of high precision and high speed rotation, respectively.

Due to the structure of the bearing, the rolling bearing is difficult to rotate at high speed because the product of the diameter of the raceway in which rolling elements such as balls rotate and the number of revolutions is limited to a certain limit value. Further, since mechanical contact is unavoidable, high-speed rotation causes a large amount of vibration and noise, and a short life due to wear or the like poses a problem, which is inappropriate for high-speed rotation of 10,000 rpm or more. .

Since the oil bearing is mechanically non-contact,
The rotation accuracy is good. However, since oil is a viscous fluid, as the rotation speed increases, viscous friction resistance increases in the oil film between the rotating shaft and the bearing bush, power consumption increases, and heat generation increases, causing thermal deformation errors. Cause
After all, it is not suitable for the operation of 10,000 rpm or more.

In the oil bearing, it is extremely difficult to seal the working oil leaking from the bearing clearance with a non-contact mechanism that does not affect the rotation accuracy. When an oil bearing is used to support the main shaft of a machine tool, the leaked hydraulic oil is generally drained. This is poured into a cutting agent tank together with cutting chips and cutting fluid, oil is separated and collected by an oil / water separator, etc., and further highly filtered to remove impurities and reused as working oil for oil bearings.

Since this is a large-scale method and is economically burdensome, most of the cases do not collect the hydraulic oil but make it disposable. Further, in a machine tool using an oil bearing, the operating oil is spilled, so that useless oil adheres to the work piece, its handling is uncomfortable, and the working environment tends to deteriorate. As described above, it has been difficult to ensure high rotation and high accuracy in the rolling bearing and the oil bearing.

(Regarding Air Bearing) On the other hand, the air bearing applies air pressure to the bearing clearance between the bearing bush and the rotary shaft to float the rotary shaft from the bearing bush, and is suitable for high precision and high speed rotation. ing. Further, in the air bearing, the discharged is clean air, which does not pollute the work piece or the working environment, nor does it need to be recovered. It can be said that it is a bearing that is kind to people and the earth.

However, it is difficult to increase the load with an air bearing, and in a machine tool, high precision on the order of micron, high rotation of about tens of thousands of revolutions, and cutting of a general metal with a depth of several millimeters of several meters per minute. It is difficult to realize high-efficiency machining by satisfying all conditions of high load corresponding to machining.

The air bearing is classified into a dynamic pressure type and a static pressure type based on the principle of floating the rotating shaft. A dynamic pressure type air bearing forms a wedge-shaped clearance in the bearing clearance so that the air near the surface of the rotating shaft is drawn into the bearing clearance due to its viscosity as the rotating shaft rotates, and the pressure for floating the rotating shaft is reduced. appear. Therefore, it is not suitable for a spindle support of a machine tool, although it is used for a device or the like that has no levitation force when the rotary shaft is stopped and does not repeatedly start and stop.

In the static pressure type air bearing, a throttle is formed in the air supply path from the outside to the bearing clearance, and pressurized air is introduced into the bearing clearance through this throttle, and the main shaft is levitated by the static pressure. Yes, a constant levitation force can be obtained regardless of the rotation speed. Therefore, the static pressure type is suitable for the spindle support of machine tools.

The static pressure air bearing is classified into a porous throttle type, a slot throttle type, a surface throttle type, and a multi-hole supply hole type, depending on the type of air supply. In the porous throttle type, a porous material is provided so as to face the bearing clearance, and air from the outside is blown into the bearing clearance to pass through the porous material. It has high rigidity and high-speed stability. However, it is difficult to obtain a proper porous material and it is difficult to process it.

In the slot throttle type, the opening of the air supply path leading to the bearing clearance is formed in a narrow slot shape, but it is difficult to accurately process the width and length of the slot. In the surface drawing type, a bearing surface facing the bearing clearance is provided with an extremely thin groove communicating with the air supply path, and the resistance when passing through this groove causes a throttling effect, but the bearing clearance is extremely small and the machine tool Is not suitable for spindle bearings.

The multiple air supply hole system is further classified into an orifice diaphragm system, a capillary diaphragm, and a self-made diaphragm. The orifice throttle forms an orifice in the vicinity of the bearing clearance of the air supply path. However, if the relationship between the capacity of the pocket (the space generated on the bearing clearance side of the orifice), the throttle diameter, and the working pressure is not appropriate, the pneumatic hammer ( Self-excited vibration) is likely to occur and is unstable.

The capillary throttle is an article in which the air supply path leading to the bearing clearance is made extremely fine to obtain the throttle effect, but its manufacture is difficult and it is not practical. The self-throttled type is a product in which the portion near the bearing clearance of the air supply path is made thin, and the diaphragm effect is obtained by a virtual cylindrical surface formed by this thin air supply path and the bearing clearance. Most suitable for.

(Setting of Bearing Clearance) In a rotary bearing, enormous air supply energy is required to increase the distance between the rotary shaft and the bearing bush (bearing clearance, that is, the floating amount of the rotary shaft). For this reason, the bearing clearance of the conventional air bearing is set to a small value of about 5 to 10 microns on one side (when the rotating shaft is at the bearing center).

(About double row type air bearing) In a cylindrical type air bearing that supports a rotary shaft in a radial direction, the bearing bush is accurately press-fitted and assembled in the housing, so that the axial dimension has a certain length (for example, a certain length). The length is preferably equal to or larger than the outer diameter of the bearing bush). In order to effectively use this length to improve the bearing performance, in one bearing bush, the throttle holes (air nozzles) arranged in the circumferential direction are arranged in two rows in the axial direction. Air system or double-row air supply system with more than one line.

[0019]

However, in a double-row type air bearing, even if a plurality of air nozzle rows are simply formed in one bearing bush, the effect of two air bearings may not be obtained. . For example, in FIG. 5, an air bearing 90 is a self-made throttle type aerostatic bearing that radially supports a main shaft 91 of a machine tool, and a bearing bush 92 has two rows of air nozzles 93 arranged in the circumferential direction. 94 are formed.

The air from the air nozzles 93, 94 is blown into the inner surface of the bearing bush 92 to support the main shaft 91 with the outer peripheral surface of the main shaft 91, and to both ends of the bearing bush 92 opened to the outside. It flows toward and is discharged outside. Therefore,
Normally, the pressure between the inner circumference of the bearing bush 92 and the outer circumference of the main shaft 91 (schematically represented by a large number of arrow rows) is
Since it is in a sealed state with respect to the outside between 4 is constant at P1, but in the portion between each air nozzle 93, 94 and the end of the bearing bush 92 due to the outflow to the outside each air nozzle 93, 9
4 side is P1, but at the end of the bearing bush 92 that is open to the outside, P
A pressure curve (shown by a one-dot chain line in FIG. 5) inclined so as to be 0 is drawn.

Here, in the case of a general one-row nozzle air bearing, if the main shaft is displaced in the radial direction by an external force or the like, the bearing clearance becomes small on the side where the main shaft is close, and the air flow resistance is large. As a result, the pressure between the inner circumference of the bearing bush and the outer circumference of the spindle increases. On the other hand, on the side where the main shaft is separated, the bearing clearance increases, the air flow resistance decreases, and the pressure between the inner circumference of the bearing bush and the outer circumference of the main shaft decreases. As a result, the spindle receives a force opposite to the displacement,
It is restored to the original bearing center. This is the bearing rigidity of the air bearing.

However, in the above-described two-row type bearing 90 of FIG. 5, since the section between the air nozzles 93 and 94 is not open to the outside air, there is no air flow and the pressure P1 does not change. Then, the above-described change in pressure (a circular arc-shaped pressure curve) occurs only in the section from the air nozzles 93, 94 to the end of the bearing bush 92, and the pressure increases on the upper side of FIG.
On the lower side, the pressure is reduced and a restoring force of the spindle 91 is generated. Therefore, the restoring force can be obtained only in a short section from each air nozzle 93, 94 to the end of the bearing bush 92, and although the air nozzle is long in two rows and contributes to the improvement of the bearing rigidity. There was a problem not to do.

In addition to the above-mentioned problems, in the air bearing, if the bearing clearance is small, the following problems occur. (Problem of allowable displacement amount) When the bearing clearance is small, the allowable displacement amount of the rotating shaft (the allowable displacement amount of the central axis position) becomes small.

When the permissible displacement amount of the rotating shaft becomes small, the rotating shaft comes into contact with the bearing bush even with a small external force, and when the rotating shaft comes into contact with the bearing bush at a high speed, frictional heat causes instantaneous seizure (welding), which causes the operation. In addition to being forced to stop, the restoration requires a great deal of labor and expense.

Due to such a restriction of the allowable displacement amount, the conventional use of the air bearing for the machine tool is precise and quiet, but the use for light load cutting (for example, an aluminum alloy or the like is performed at a depth of several microns at a few minutes per minute). It is limited to a feed of 10 mm), and it was desired to be applied to heavy cutting where the load that displaces the spindle becomes large.

(Problem of obstacle due to foreign matter) In the air bearing, when foreign matter is mixed in the air flowing into the bearing clearance, if the bearing clearance is small, even a minute foreign matter is caught in the bearing clearance. However, there is a possibility of causing the above-mentioned operation failure such as seizure.

(Problem of heat generation due to shearing of air) If the bearing clearance is small, the air in this clearance is likely to generate heat due to shearing force between the rotating shaft side and the bearing bush side. Then, this heat generation causes thermal deformation, which may reduce accuracy.

The above-mentioned problems are matters in which the conventional air bearing is applied to the machine tool only for quiet and light cutting, so that no trouble is caused. However, when considering application to intermittent high-load cutting such as end milling, it is important to increase the bearing clearance.

An object of the present invention is to provide a spindle head for a machine tool which can support the main shaft of the machine tool with sufficient bearing rigidity and can rotate at high speed with high accuracy and high load.

[0030]

According to the present invention, a double row type air bearing is used to support a spindle in a spindle head for machine tools, and means for discharging air to the outside is provided between a plurality of air nozzle rows. Thus, when the main shaft is eccentric, a restoring force is also generated between the air nozzle rows to increase the bearing rigidity. Specifically, the present invention is a machine tool having a main shaft that is rotationally driven by a drive source, at least one air bearing that supports the main shaft in its radial direction or axial direction, and a housing that accommodates the air bearing. A spindle head for use, wherein the air bearing is a self-throttled aerostatic pressure bearing, and a single bearing bush is a double row air bearing in which two or more rows of air nozzles are arranged. It is characterized in that an escape portion for discharging air is provided between the rows.

In the present invention as described above, the main shaft is supported by the air bearing in the housing, and high-precision and high-speed rotation is possible. Here, a single bearing bush is provided with a plurality of air nozzle rows, and normally air cannot escape to the outside in this section. However, in the present invention, the air discharge rows are provided in a portion between the air nozzle rows. Since the part is formed,
Air from each air nozzle row is exhausted to the outside air through the relief part, and when the main shaft is eccentric, pressure fluctuations also occur in this section depending on the bearing clearance, and the restoring force of the main shaft is stronger than when there is no relief part as a whole. To be done. As a result, the bearing rigidity is increased, it is possible to cope with a high load, and it is possible to achieve the above-mentioned object together with high-speed rotation and high accuracy.

The air bearing preferably has a bearing bush made of a sintered carbon material. By doing so, it is possible to reduce the frictional resistance in the contact state by utilizing the self-lubricating property of the sintered carbon material. That is, it is possible to prevent seizure even if the main shaft and the bearing bush come into contact with each other when an excessive load acts due to some trouble or when the supply air pressure drops.

The air bearings are a cylindrical air bearing that supports the main shaft in the radial direction and a disk-shaped air bearing that supports the main shaft in the axial direction. The bearing bush of the cylindrical air bearing and the disk-shaped air bearing are used. It is desirable that the bearing bush of the air bearing be integrally molded. With this configuration, the press-fitting length of the cylindrical air bearing into the housing can be made large, and the deformation of the bearing can be prevented, the accuracy can be improved, and the mounting can be ensured.

That is, the air supply groove is formed on the back surface of the disk-type air bearing bush, and when the supply air pressure acts on the air supply groove, the bearing bush press-fitted into the housing receives a force in the axial direction, that is, the direction in which it is removed. . In particular, when it is made of a sintered carbon material having a small friction coefficient, a sufficient press-fitting length is taken, and unless the press-fitting friction force is provided, the clearance of the disk type air bearing changes due to the press-fitting out. However, as described above, by integrating the disc shape and the cylindrical shape, the press-fitting length can be increased, and this problem can be solved.

It is preferable that the portion of the main shaft supported by the air bearing is surface-treated with a non-rusting high hardness material. As the surface treatment with a non-corrosive high hardness material, chromium plating, nickel / phosphorus electroless plating, nickel / phosphorus particle dispersed electroless plating, etc. can be used.

By doing so, it is possible to reduce the occurrence of rust on the surface as compared with a spindle that has been frequently used conventionally (made of stainless steel, the surface of which is hardened, etc.), and rust interferes with the bearing clearance as foreign matter. Can be prevented. Further, it is possible to reliably obtain the effect of generating rust on various materials, and it is possible to use other materials having a low expansion coefficient in order to reduce thermal deformation.

A bearing bush of the air bearing is press-fitted and held in the housing, an air supply path for supplying air to the air bearing is formed in the housing, and the housing is preferably made of stainless steel. . By doing this, it is possible to prevent rust from occurring on the air supply path due to the stainless steel housing and the press fit of the bearing bush.
It is possible to prevent rust from entering the bearing clearance from the air supply path and causing a failure.

It is preferable that the drive source is a built-in motor formed in the housing, and that the housing has an exhaust path through which the air from the air bearing is discharged via the built-in motor. With this configuration, the spindle head can be downsized and the structure can be simplified by the built-in motor, and the built-in motor can be cooled by exhaust air from the air bearing. Particularly, in the present invention, since the bearing clearance is large, the amount of ventilation is increased, and the cooling effect can be increased.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a machine tool spindle head 10 includes a housing 20, a spindle 30, a built-in motor 40, and air bearings 50 and 60.

(Outline of each part) The housing 20 is supported by a column or the like of a machine tool (not shown) and is moved relative to the work on the table. The spindle 30 has a disk-shaped flange 31 in the middle part, and the middle part is a housing.
It is rotatably supported by a radial air bearing 50 and an axial air bearing 60 formed inside 20.

The radial air bearing 50 is a flange of the main shaft 30.
There are five rows, one row on the tip side and four rows on the base side rather than 31. The axial air bearing 60 is provided with a pair of two rows so as to sandwich the flange 31. A chuck mechanism or the like (not shown) is formed at the tip of the main shaft 30, and a tool such as a blade is attached via this chuck mechanism, and the built-in motor 40 drives the tool to rotate the workpiece. And so on.

The built-in motor 40 has a rotor 41 and a stator 42. The rotor 41 is connected to and supported by the end of the main shaft 30. The stator 42 is arranged so as to surround the rotor 41, and receives electricity from an external control device (not shown) to rotate the rotor 41, whereby the main shaft 30 is rotated.

Such a built-in motor 40 has a cover 29.
It is surrounded by. The cover 29 supports the stator 42 on the inner side surface and covers the rotor 41 and the stator 42 by connecting the flange 291 to the end of the housing 20. The outer peripheral portion of the cover 29 is surrounded by a water jacket 43 for cooling the built-in motor portion.
The cover 29 constitutes a part of the housing 20.

(Details of Air Bearing) The housing 20 has a cylindrical first member 21 and a second member 22 fitted to the outer periphery thereof, and is provided on the tip side of the main shaft 30 of the first cylindrical body 21. Large diameter part at the end
211 is formed. Then, the fourth member 24 is attached to the large-diameter portion 211 via the third member 23.

A step portion is formed inside the first member 21 on the base end side of the main shaft 30, and the first bearing bush 25 is formed in this step portion.
Are fitted. A step portion is also formed on the large diameter portion 211 side, and the second bearing bush 26 is fitted in this step portion. The second member 22 has a water jacket for cooling the bearing portion formed therein. Inside the fourth member 24, from the side connected to the large diameter portion 211 to the third bearing bush 2
7 is fitted.

(Details of Bearing Bush) First Bearing Bush
25 forms two rows of radial air bearings 50,
Air nozzles 51 are arranged in two rows at predetermined intervals in the circumferential direction on the first bearing bush 25. The air nozzle 51 penetrates the outer circumference and the inner circumference of the first bearing bush 25 in the radial direction of the main shaft 30. Inside the first bearing bush 25, an exhaust groove 52 continuous in the circumferential direction is formed in the middle of each row of the air nozzles 51 as an air discharge escape portion, and the exhaust groove 52 penetrates to the outer periphery. An exhaust hole 53 is formed.

The second bearing bush 26 forms two rows of radial air bearings 50 and one axial air bearing 60 of the pair, and is fitted to the end surface of the first member 21 on the large diameter portion 211 side. It has a flange 261 that fits in. In the second bearing bush 26, the air nozzles 51 are arranged in two rows at predetermined intervals in the circumferential direction,
Flange 261 formed at the end of the third bearing bush 27 side
The air nozzles 61 are arranged at predetermined intervals in the circumferential direction. The air nozzle 51 penetrates the outer circumference and the inner circumference of the second bearing bush 26 in the radial direction of the main shaft 30, and the air nozzle 61 penetrates the front and back of the flange 261 in the axial direction of the main shaft 30.

Inside the second bearing bush 26, an exhaust groove 52 continuous in the circumferential direction is formed in the middle of each row of the air nozzles 51 as an air discharge escape portion. An exhaust hole 53 penetrating therethrough is formed. A notched exhaust groove 62 that is continuous over the entire circumference is formed on the inner peripheral edge of the end of the second bearing bush 26 on the flange 261 side.

The third bearing bush 27 forms one row of radial air bearings 50 and the other axial air bearing 60 of the pair, and is fitted to the end surface of the fourth member 24 on the third member 23 side. It has a recessed flange 271. Air nozzles 51 are arranged in a row in the third bearing bush 27 at predetermined intervals in the circumferential direction,
Flange 271 formed at the end of the second bearing bush 26 side
The air nozzles 61 are arranged at predetermined intervals in the circumferential direction.

This air nozzle 51 penetrates the outer circumference and the inner circumference of the third bearing bush 27 in the radial direction of the main shaft 30, and
Reference numeral 61 penetrates the front and back of the flange 271 in the axial direction of the main shaft 30. A notched exhaust groove 62 that is continuous over the entire circumference is formed on the inner peripheral edge of the end of the third bearing bush 27 on the flange 271 side.

(Air Supply Path) Two air supply grooves 212 continuous in the circumferential direction are formed on the inner periphery of the portion of the first member 21 where the first bearing bush 25 is fitted, and each air supply groove 212 is formed. Is each air nozzle 51
Is positioned so as to communicate with the outer opening of the. Two air supply grooves 212, 213 continuous in the circumferential direction are also formed on the inner periphery of the portion of the first member 21 where the second bearing bush 26 is fitted,
The air supply grooves 212, 213 are arranged at positions that communicate with the outer openings of the air nozzles 51 of the second bearing bush 26. The air supply groove 213 is extended to the end surface on the flange 261 side and communicates with each air nozzle 61 formed on the flange 261.

The first member 21 has one communicating hole 2 from the base end side.
14 is formed, and this communication hole 214 communicates with all of the four air supply grooves 212, 213. The opening on the base end side of the communication hole 214 is closed by a sealing member 2141. Air supply groove 213
An air supply hole 215 is radially penetrated from the outer circumference of the large diameter portion 211. Therefore, in the first member 21, by supplying the pressurized air from the air supply hole 215, this air is supplied to the air nozzle 61 from the air supply groove 213, and further from the communication hole 214 to the air via each air supply groove 212. It is adapted to be supplied to the nozzle 51.

An air supply groove 243 that is continuous in the circumferential direction is also formed in the inner circumference of the portion of the fourth member 24 where the third bearing bush 27 is fitted, and this air supply groove 243 is formed in each of the second bearing bushes 26. The air nozzle 51 communicates with the outer opening and also communicates with each air nozzle 61 formed on the flange 271. A communication hole 244 that connects the air supply groove 243 and the end surface on the side of the third member 23 is formed in the fourth member 24, and a communication hole 234 that communicates with this communication hole 244 is formed in the third member 23. A communication hole 216 that connects the communication hole 234 and the air supply hole 215 is formed in the large-diameter portion 211 of 21. Therefore, in the fourth member 24, the first member 21
By supplying the pressurized air from the air supply hole 215 of this, this air is supplied to the air supply groove 243 through the respective communication holes 216, 234, 244, and is supplied to the air nozzles 51, 61. .

(Exhaust path) The first member 21 is formed with two exhaust holes 217 communicating with the exhaust grooves 52 of the first bearing bush 25 and the second bearing bush 26.
An exhaust hole 218 communicating with the inner peripheral side is formed in the section between 6. A communication hole 219 is formed so as to communicate these exhaust holes 217 and 218. One end of the communication hole 219 is opened at the end surface on the third member 23 side, and the other end is opened at the end on the built-in motor 40 side.

The third member 23 has an exhaust hole 23 communicating with the inner peripheral side.
1 is formed, and this exhaust hole 231 is a communication hole 219 of the first member 21.
It is also connected to. Cover for built-in motor 40
A notch-shaped exhaust groove 292 is formed continuously around the inner periphery of 29, and the exhaust groove 292 communicates with the communication hole 219 of the first member 21. An exhaust hole 293 communicating with the outside is formed at the center of the end surface of the cover 29.

Therefore, the air supplied to each of the air nozzles 51 and 61 described above is transmitted to the inner surface of each bearing bush 25, 26 and 27 and the main shaft.
Through the gap between the circumferential surface of 30 or the surface of the flange 31, flows between the exhaust grooves 52, 62, the bearing bushes 25, 26, and inside the third member 23, and any of the exhaust holes 217, 218, 231. It is collected from there to the communication hole 219. Then, the gas is discharged from the exhaust groove 292 through the inside of the cover 29 (the gap of the built-in motor 40) to the outside by the exhaust hole 293.

(Setting of air bearing) Between the first to third bearing bushes 25, 26 and 27 and the peripheral surface of the main shaft 30, there are cylindrical portions between the ends of the bushes and the exhaust grooves 52 and 62, respectively. Self-throttled static pressure radial air bearing with air nozzle 51
The air bearing 50 supports the main shaft 30 in the radial direction. Second and third bearing bushes 26, 27
Between the outer peripheral edge of the flange 31 and the exhaust groove 62 between the main shaft 30 and the surface of the flange 31 of the main shaft 30.
A self-made throttle static pressure type axial air bearing 60 is constituted by 61, and the main shaft 30 is axially supported by the air bearing 60.

Here, in each bearing 50, 60, the throttle diameter of each air nozzle 51, 61 is set to 400 to 800 microns. Further, the radial bearing clearance Cr when the main shaft 30 is in the center of the air bearing 50 and the axial bearing clearance Ca when the flange 31 is in the center of the air bearing 60 are each set to 15 to 30 μm on one side. There is.

The bearing bushes 25, 26, 27 are made of a sintered carbon material, and the first member 21,
It is fixed to the fourth member 24 by press fitting. Then, among the respective members forming the housing 20, the first member 21 and the fourth member in which the air supply paths such as the communication holes 214 and 219 and the exhaust paths are formed.
24 are each made of stainless steel.

The portion of the peripheral surface of the main shaft 30 supported by the air bearing 50 and the portion of the surface of the flange 31 supported by the air bearing 60 are chromium plated, nickel-phosphorus electroless plated, nickel-plated, respectively. Surface treatment with non-corrosive high hardness material such as phosphorus particle dispersion electroless plating is performed.
Further, the main shaft 30 is made of iron, amber (an alloy of iron and nickel), or the like, but in the present embodiment, the main shaft 30 is made of amber having a smaller coefficient of thermal expansion than iron or the like. This makes it possible to reduce the amount of thermal deformation of the main shaft 30 itself.

In each bearing bush 25, 26, the section distance between the air nozzle 51 of each air bearing 50 and the end of the bearing bush 25, 26 or the exhaust groove 52 is the same as that of each air nozzle 51, 61. Be equal on both sides. In particular,
As shown in FIG. 2, the axial distances A1, A2, A3, A4 are all equal. In each bearing bush 26, 27, the section distance B1, B2 between the air nozzle 61 of each air bearing 60 and the outer peripheral edge of the flange 31 or the exhaust groove 62 (see FIG. 3).
Are equal on both sides of each of the air nozzles 51 and 61, and also on the opposing air bearings 60.

(Operation of Exhaust Groove) In this embodiment, the main shaft 30 is supported by the air bearings 50, 60 in the housing 20 in the radial direction and the axial direction with high precision, and is rotated at a high speed by the built-in motor 40. It At this time, as shown in FIG. 2, in the bearing bush 25 of the present embodiment, the two rows of air bearings 5 are used.
High-pressure air is supplied from each of the two rows of air nozzles 51 forming 0, and this air is supplied to the inner peripheral surface of the bearing bush 25 and the main shaft.
The main shaft 30 floats and supports by flowing into the outer peripheral surface of 30 (bearing clearance).

In each of the air bearings 50, the air that has flowed into the bearing clearance is divided into air nozzles 51 on both sides in the axial direction, and one flows out from the end of the bearing bush 25 to the outside of the bush, while the other exhausts. It flows into the groove 52 and is discharged through the bush hole or the exhaust hole 217. The air flowing out to the left side of the bearing bush 25 in the figure passes through the exhaust hole 218 communicating with the inside of the first member 21 and the exhaust hole 217.
The air discharged from the communication hole 219 to the inside of the cover 29 together with the exhaust air, and the air flowing out to the right side in the drawing is directly discharged into the cover 29 and released to the outside air.

Therefore, in each of the two rows of air bearings 50 formed in the bearing bush 25, the inner circumference of the bearing bush 25 and the main shaft 30
The pressure between the outer circumference and the outer circumference (schematically indicated by a large number of arrows) is as follows. At the portion between each air nozzle 51 and the end of the bearing bush 25, each air nozzle 51 is caused by the outflow to the outside.
At the end of the bearing bush 25, which is open to the outside at P1, the pressure curve (indicated by the one-dot chain line in FIG. 2) is inclined so that it becomes P0. This is similar to the conventional bearing shown in FIG.

In the portion between the air nozzles 51, the exhaust groove 52
The air in the relevant part is discharged by the
On the exhaust groove 52 side at P1, a pressure curve (indicated by a dashed line in FIG. 2) that is inclined so as to become P0 is drawn. This is significantly different from the conventional bearing shown in FIG. 5 described above (constant at pressure P1 because it is not exhausted at that portion).

Therefore, in the present embodiment, the spindle 30
Is displaced in the radial direction by an external force or the like, in the bearing bush 25 of FIG. 2, the change in pressure according to the change in bearing clearance is not limited to the section from each air nozzle 51 to the end of the bearing bush 25. It also occurs between the air nozzles 51 (a section from each air nozzle 51 to the exhaust groove 52).

That is, in FIG. 2, the main shaft 30 is displaced to the upper side in the figure, and as a result, the pressure increases (up to a circular arc shape) in the upper side of FIG. 2 in a total of four sections on both sides of each air nozzle 51. Pressure curve), the pressure decreases on the lower side (it becomes a pressure curve that is recessed in an arc shape), and each difference (it becomes an oblique spindle-shaped region shown by the dotted line on the lower side of FIG. 2)
Acts as a restoring force of the spindle 30.

This means that a restoring force twice as large as that of the conventional air bearing of FIG. 5 is generated, and the restoring force is the bearing bush.
By using almost the entire length of 25 and the entire axial length of the two rows of air bearings 50, it is possible to improve the bearing rigidity. At this time, since the axial distances A1, A2, A3, A4 are all made equal, the restoring forces in the respective sections are made substantially equal, and an unnecessary moment or the like is not generated in the main shaft 30.

Although the two rows of air bearings 50 in the bearing bush 25 have been described above, the bearing bush 26 having the exhaust groove 52 between the two rows of air bearings 50 can also provide the same operation. The bearing bush 26 is a three-row air bearing mechanism in which two rows of radial air bearings 50 and axial air bearings 60 are integrally formed.
Exhaust is also performed by the exhaust groove 62 in the portion between them, and the same operation as that of the exhaust groove 52 described above is achieved. Therefore, the bearing rigidity can be increased by effectively utilizing the axial length and diameter of the bearing bush 26. Bearing bush
Also in 27, exhaust is performed by the exhaust groove 62 between the air bearings 50 and 60, and the same operation as that of the corresponding portion of the bearing bush 26 is achieved.

(Effect of this Embodiment) In this embodiment, the main shaft 30 has the air bearings 50 and 6 in the housing 20.
Since the exhaust grooves 52, 62 are provided between 0, the bearing bushes 25, 26,
A bearing as a double-row type air bearing mechanism that is capable of sufficiently generating a restoring force at the time of displacement of the main shaft in each of the plurality of air bearings 50, 60 provided on the 27, and is constituted by the bearing bushes 25, 26, 27. The rigidity can be increased. In addition, each air bearing
Bearing clearances Cr and Ca of 50 and 60 are 15 to 15 on each side.
Since it is 30 microns, which is more than double that of the conventional one, the allowable displacement amount can be expanded, and the problem of foreign matter, air heat generation, etc. can be solved.

Further, the self-restriction type aerostatic pressure bearing is adopted as the air bearings 50 and 60, and the sufficient bearing rigidity is secured by setting the throttle diameter and the bearing clearances Cr and Ca to the above-mentioned values. You can Therefore, it becomes possible to cope with a sufficiently high load as the spindle head 10 for machine tools, and in addition to the characteristics of an air bearing, such as high speed rotation and high accuracy, not only light cutting but also precision heavy cutting can be performed.

As an example, for the air bearing 50, 60 mm
Diameter, number of air nozzles 51 / row, hole diameter of air nozzles 51 500
It was manufactured with a micron, and the actual measurement was performed at a supply air pressure of 6 kgf / square cm. FIG. 4 shows the results. In FIG. 5, the measured bearing stiffness curve 99 shows that the bearing rigidity exceeds 3 kgf / micron in the bearing clearance range of 16 to 29 microns, and the bearing rigidity is 4 kgf / micron in a wide range of the bearing clearance of 18 to 26 microns. Is over. From this, it can be understood that the effectiveness of the setting according to the present invention as an air bearing and the high bearing rigidity can be easily obtained.

In this embodiment, each bearing bush 25, 2
Since 6 and 27 are made of sintered carbon material, each air bearing 5
In Nos. 0 and 60, the frictional resistance in the contact state can be reduced by utilizing the self-lubricating property of the sintered carbon material. That is, if an excessive load is applied due to some malfunction, or if the supply air pressure drops, the main shaft 30 and bearing bush 25
It is possible to prevent the occurrence of seizure even when ~ 27 is in contact.

Since both the cylindrical air bearing 50 that supports the main shaft 30 in the radial direction and the disk-shaped air bearing 60 that supports the main shaft 30 (flange 31) in the axial direction are provided, the radial direction and the shaft The above-mentioned excellent bearing performance can be demonstrated in each direction. Furthermore, in the second and third bearing bushes 26, 27, the bearing bush of the radial air bearing 50 and the bearing bush of the axial air bearing 60 are integrally formed, so that the housing 20 of the air bearing 50 portion is formed. The press-fitting length into the (first member 21) can be made large, and the deformation of the bearing can be prevented, the accuracy can be improved, and the mounting can be ensured.

That is, the disk type air bearing bushes 26, 2
Air supply grooves 213 and 243 are formed on the back surface of 7, but when the supply air pressure acts on the air supply grooves 213 and 243, the bearing bushes 26 and 27 press-fitted into the housing 20 receive a force in the direction of removal. In particular, when it is made of a sintered carbon material having a small friction coefficient, the press-fitting length is sufficient, and the clearance Ca changes unless the press-fitting friction force is applied. However, as described above, by integrating the disc shape and the cylindrical shape, the press-fitting length can be increased, and this problem can be solved.

Further, since the portion of the main shaft 30 supported by the air bearings 50 and 60 is subjected to a surface treatment with a non-corrosive high hardness material, the occurrence of rust on the surface can be reduced, and the rust as a foreign matter causes the bearing clearance Cr. , Ca can be prevented from causing a disorder. Further, it is possible to reliably obtain the effect of generating rust on various materials, and it is possible to use other materials having a low expansion coefficient in order to reduce thermal deformation.

Further, bearing bushes 25, 26, 27 are press-fitted and held in the first member 21 and the fourth member 24 of the housing 20,
These first member 21 and fourth member 24 have air bearings 50, 6
Air supply path for supplying air to 0 (communication hole 214, air supply groove 212
Etc. are formed and the first member 21 and the fourth member 24 are formed of stainless steel, so that rust can be prevented from occurring on the air supply path, and rust can be generated from the air supply path to the bearing clearance. It is possible to prevent invasion into Cr and Ca to cause damage.

In the present embodiment, since the built-in motor 40 formed in the housing 20 is used as the drive source of the main shaft 30, the built-in motor 40 can downsize the spindle head, simplify the structure, and prevent the main shaft 30 from contacting. Can be supported by. Further, the air bearings 50, 6 are provided on the first member 21, the third member 23, and the cover 29 of the housing 20, respectively.
Since the exhaust path (communication hole 219 and the like) for discharging the air from 0 through the built-in motor 40 is formed, the built-in motor 40 can be cooled by the exhaust from the air bearings 50 and 60. In particular, in the present embodiment, the bearing clearances Cr and Ca are made larger than in the conventional case, so that the ventilation amount is increased and the cooling effect can be made large.

It should be noted that the present invention is not limited to the above-described embodiment, and the following modifications and the like are also included in the present invention. In the above embodiment, the radial air bearing 50 is formed in one bearing bush 25, 26, 27 in two rows or one row, but the number of rows may be appropriately changed, such as three rows or more, or only one row. It is a thing. The number of air nozzles 51 in each row can be set as appropriate for implementation. A plurality of air bearings are formed on at least one bearing bush,
The present invention is included in the present invention as long as it forms an air exhaust relief portion such as an exhaust groove in between.

The air discharge relief portion is not limited to the exhaust grooves 52 and 62 as described above, but may have a structure in which exhaust slits extending in the circumferential direction are arranged, a structure in which a large number of exhaust holes are arranged in a band, or the like. Well, in short, any structure that can discharge the air in the section between the two air bearings may be used. For this reason, one exhaust hole or the like may be provided between the two air bearings, but it is desirable to dispose them evenly in the circumferential direction in consideration of the pressure balance in the circumferential direction.

Further, the axial air bearing 60 has the flange 31
Although one pair is arranged in one row with the column sandwiched in between, two or more rows may be formed concentrically. Further, the flanges 31 may be arranged at two or more places on the main shaft 30, and each of them may be supported by the radial air bearing 60.

Also, the second and third bearing bushes 26, 2
In Fig. 7, the radial air bearing 50 and the axial air bearing 60 are integrally formed. However, separate bearing bushes may be used for these. Further, the number of bearing bushes formed to support the main shaft 30 is not limited to the first to third three as in the above embodiment, but may be two or less or three or more. These bearing bushes 25, 26, 27 may be fixed to the first member 21 and the fourth member 24 of the housing 20 by press-fitting or other fixing means such as screwing.

The structure of the housing 20 is not limited to the structure of the first to fourth members 21 to 24 and the cover 29 as in the above-described embodiment, but may be a combination of fewer members or more members, or another divided form. Alternatively, the cover 29 that covers the built-in motor 40 may be omitted as appropriate. In the above-described embodiment, the exhaust from each air bearing 50, 60 is used for cooling by passing through the built-in motor 40, but instead of passing through the built-in motor 40, the air may be exhausted directly to the outside through the communication hole 219 or the like. Good.

The bearing bushes 25, 26, 27 may be made of other material such as stainless steel instead of the sintered carbon material. However, a material that has the desired strength and does not rust,
Alternatively, a material having a self-lubricating property is desirable. The surface of the main shaft 30 supported by the air bearings 50 and 60 was surface-treated with a non-rusting high hardness material.
You may go to the entire surface. Further, when the main shaft 30 is made of a non-rust material such as stainless steel, it may be omitted as appropriate. The material of the housing 40 is not limited to stainless steel and may be plastic or the like. However, it is desirable that the portion where the air supply path is formed does not rust and that it has the desired strength.

[0085]

As described above, according to the present invention,
High precision and high speed rotation can be realized by supporting the main shaft by the air bearing in the housing. Here, by forming a plurality of air bearings in the bearing bush, and forming an air discharge relief portion between the air nozzles of each air bearing to exhaust air in the relevant section, the restoring force at the time of displacement of the spindle axis Can be ensured and the bearing rigidity can be increased, and by these, high load, high speed rotation, and high precision can be realized in the spindle head for machine tools.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a main part of a radial air bearing in the embodiment.

FIG. 3 is an enlarged sectional view showing a main part of an axial air bearing in the embodiment.

FIG. 4 is a graph showing measured values of the air bearing according to the embodiment.

FIG. 5 is an enlarged cross-sectional view showing a main part of a conventional air bearing.

[Explanation of symbols]

 10 Machine tool spindle head 20 Housing 25, 26, 27 Bearing bush 30 Spindle 40 Built-in motor 50 Radial air bearing 60 Axial air bearing 51, 61 Air nozzle 52, 62 Exhaust groove for air discharge

Claims (6)

[Claims] 1. A spindle head for machine tools, comprising: a main shaft that is rotationally driven by a drive source; at least one air bearing that supports the main shaft in its radial or axial direction; and a housing that houses the air bearing. The air bearing is a self-restricting aerostatic pressure bearing, and is a double row air bearing in which two or more rows of air nozzles are arranged in one bearing bush, and between these air nozzle rows. A spindle head for machine tools, characterized in that a relief portion for air discharge is provided in the. 2. The spindle head for a machine tool according to claim 1, wherein the air bearing has a bearing bush formed of a sintered carbon material. 3. The spindle head for a machine tool according to claim 2, wherein the air bearing includes a cylindrical air bearing that supports the spindle in a radial direction, and a disk-shaped air bearing that supports the spindle in an axial direction. A spindle head for a machine tool, wherein the bearing bush of the cylindrical air bearing and the bearing bush of the disk air bearing are integrally formed. 4. The spindle head for a machine tool according to claim 1, wherein a portion of the main shaft supported by the air bearing is surface-treated with an antirust high hardness material. A spindle head for machine tools that is characterized by 5. The spindle head for a machine tool according to claim 1, wherein a bearing bush of the air bearing is press-fitted and held in the housing, and the air bearing is installed in the air bearing in the housing. A spindle head for a machine tool, characterized in that an air supply path for supplying air is formed, and the housing is made of stainless steel. 6. The spindle head for a machine tool according to claim 1, wherein the drive source is a built-in motor formed in the housing, and the housing includes the air bearing A spindle head for a machine tool, wherein an exhaust path for discharging the above air through the built-in motor is formed.