JP4124977B2 - Rotating device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improved rotating device used for a spindle, an indexing plate and the like of a machine tool.
[0002]
[Prior art]
Conventionally, a machine tool that requires high machining accuracy is equipped with a rotating device including a hydrostatic bearing and a built-in motor as disclosed in Japanese Patent Application Laid-Open No. 63-186030. A conventional rotating device mounted on a machine tool will be briefly described with reference to FIG.
[0003]
As shown in FIG. 5, 1a is a thrust plate, 1b is a radial rotor, and constitutes a bobbin-like rotating shaft (shaft body), which is fixed to the housing 2 and jets air from the surface. 3a, a radial bearing 3b is supported in a non-contact manner on the housing 2, thereby forming a hydrostatic bearing that can obtain high rotational accuracy.
[0004]
A motor coil 4a and a motor magnet 4b that constitute a drive motor are arranged outside the hydrostatic bearing, and an encoder disk 5a and an encoder detector 5b that constitute a rotational position detector are arranged on the outer side of the motor. Configure the device. In this rotating device, since the rotating part and the fixed part are completely non-contact, it is possible to obtain high rotational accuracy, durability and reliability.
[0005]
When such a rotating device is used for, for example, general front turning, the rotating device is mounted on a slide 6a that moves on a slide guide 6b, a work 7 is fixed to the end of the main shaft, and a shaft body is mounted. By rotating, the cutting tool 8 is moved in the X direction to form a plane or spherical surface having high shape accuracy and surface roughness.
[0006]
[Problems to be solved by the invention]
However, since the conventional rotating device has two thrust plates, and a motor and an encoder are arranged outside the hydrostatic bearing, the rotating device becomes longer in the axial direction. There was a drawback that the whole was large. Although there is a rotating device having a configuration with one thrust plate, a thrust bearing and a housing for sandwiching the thrust plate from both sides are required, and thus the main shaft length cannot be shortened even with this configuration. For this reason, the slider on which the rotating device is mounted, and thus the entire machine tool, becomes large.
[0007]
In addition, when trying to process a large workpiece with a horizontal machine tool, it may be impossible to process due to insufficient load capacity of the rotary shaft. Therefore, if the rotary shaft is of the vertical specification, the length of the rotary shaft is large, so the distance from the slide to the processing point is large, the processing point rigidity is lowered, and good surface roughness cannot be obtained. In addition, since the rotation axis is long in the axial direction, the moment of inertia around the X axis is large, the resonance frequency in this direction is low, and vibration may occur due to machining disturbance.
[0008]
Furthermore, the gap of the hydrostatic bearing is several μm, and in order to make this possible, sub-micron accuracy is required for parts processing and assembly. Since the rotating shaft of the conventional hydrostatic bearing is composed of a plurality of parts, very high technology is required for these processing and assembly, and the production takes time and cost.
[0009]
The object of the present invention is to solve the above-mentioned problems and to make the hydrostatic bearing structure simple, thin, and compact to facilitate machining and assembly of the hydrostatic bearing, and to vibrate even at a resonance frequency with high machining disturbance. It is an object of the present invention to provide a rotating device that is difficult to use and has high machining accuracy and that is used for a rotating device and an indexing board of a machine tool.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a rotating device according to the present invention is a rotating device comprising a housing, a hydrostatic bearing fixed to the housing, and a shaft body that is floatably supported by the hydrostatic bearing. the shaft body is a disk-shaped, and radial support by a radial static pressure bearing which is fixed to the outer peripheral portion of the disk-shaped shaft body to said housing, a thrust hydrostatic the bottom surface of the disk-shaped shaft body fixed to the housing The disk-shaped shaft body, which is thrust-supported by a pressure bearing and in which a ring-shaped magnet and a ring-shaped magnet having a polarity opposite to that of the magnet are arranged in the radial direction on the housing or the disk-shaped shaft body. It is characterized by comprising a suction means for sucking in the axial direction.
[0011]
The rotating device according to the present invention is characterized in that a driving motor and a rotational position detector are accommodated in the housing.
[0012]
The driving motor of the rotating device according to the present invention includes at least a motor magnet and a motor coil, and the motor magnet and the motor coil may be arranged concentrically, or the motor magnet is arranged on the bottom surface of the shaft body. In addition, a motor coil may be disposed at a position of the housing facing the motor magnet.
[0014]
Furthermore, the housing of the rotating device according to the present invention may be formed of a radial housing to which the radial bearing for supporting the radial support is fixed, and a thrust housing to which the thrust bearing for supporting the thrust is fixed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a first embodiment of a rotating device according to the present invention.
Reference numeral 1 denotes a shaft body of a hydrostatic bearing. The shaft body 1 is usually a simple cylindrical body, but has a disk shape because it is formed very thin in this embodiment. Reference numeral 2 denotes a housing, which includes a thrust housing 2a and a radial housing 2b. 3a is a thrust bearing, and 3b is a radial bearing, which is fixed to the thrust housing 2a and the radial housing 2b, respectively. These bearings are formed of a porous material, and air supplied from an air supply passage (not shown) is ejected from the surface of the bearing to support the shaft body 1 in a floating manner.
[0016]
Reference numeral 9 denotes a magnet portion including a ring-shaped magnet as suction means for sucking the shaft body 1 in the thrust bearing 3a direction. In the conventional hydrostatic bearing, two thrust bearings generate forces in the opposite directions in the axial direction to support the shaft body at a predetermined position (see the description of the conventional rotating device and FIG. 5). Then, since there is one thrust bearing, the shaft 1 is supported at a predetermined position in a floating state by balancing the floating force with the attractive force of the magnet. The outer peripheral surface of the shaft body 1 and the radial bearing 3b face each other to form a minute gap of several μm, and the pressure air in the gap supports the shaft body 1 in a non-contact manner in the radial direction.
[0017]
The housing 2 is composed of the thrust housing 2a and the radial housing 2b as described above for ease of actual processing. Since the thrust housing 2a has to be machined with a flatness of submicron order on the joint surface with the radial housing 2b, it needs high rigidity as a structure and has a thickness of several tens of mm in the axial direction. .
[0018]
In the present embodiment, a through hole 14 is formed by cutting through the central portion of the thrust housing 2a in a circular shape, and a motor coil 4a constituting a drive motor is incorporated along the inner peripheral wall of the through hole 14. On the other hand, the motor magnet 4b constituting the drive motor is concentrically arranged at a position facing the motor coil 4a along the outer peripheral wall of the rotating cylinder 13 extending in the axial direction from the center of the back surface of the shaft body 1. Is provided.
[0019]
In order to obtain the required motor torque, when the axial length of the motor is limited, it is necessary to expand at least the motor coil 4a in the radial direction. In this embodiment, since there is a space in the radial direction, a necessary torque can be ensured. The drive motor uses a built-in type DC brushless motor that is small, has a relatively large torque generation, is non-contact, and has high precision and excellent durability.
[0020]
In addition, by utilizing the hollow internal space of the rotary cylinder 13, an encoder disk 5a constituting a rotational position detector fixed to the shaft body 1 and an encoder detector 5b fixed to the thrust housing 2a in the space. Is placed.
[0021]
With this configuration, a motor, an encoder, or the like is provided in the thrust housing 2a without particularly increasing the axial thickness of the thrust housing 2a, that is, without increasing the axial length of the rotating device. Can be accommodated.
[0022]
Further, regarding the fact that the thrust bearing rigidity and the radial bearing rigidity are substantially equal, in this embodiment, the axial length of the hydrostatic bearing can be reduced to about ½ that of the conventional one. At this time, the increase in dimension in the radial direction is about 20 to 30%. Further, in this example, the axial length of the rotating device is the same as that of the conventional rotating device although the rigidity (thrust bearing rigidity and radial bearing rigidity) of the hydrostatic bearing is equivalent to that of the conventional one. It can be reduced to about 1/3 compared to the one.
[0023]
For example, when the diameter of the shaft body 1 is 240 mmφ and the thickness is 45 mm, the outer diameter of the rotating device is about 300 mmφ and the axial length can be very thin, about 100 mm. At this time, if the thrust bearing 3a uses a porous diaphragm having an inner diameter of 170 mmφ and an outer diameter of 240 mmφ, and the magnet 9 is a rare earth magnet having an inner diameter of 108 mmφ, an outer diameter of 166 mmφ, and a thickness of 3 mm, the gap between the magnet 9 and the shaft body 1 In the case of 0.25 mm, a suction force of about 4500 N is obtained.
[0024]
Therefore, if the load capacity of the thrust bearing 3a and the attractive force of the magnet 9 are balanced with a bearing clearance of 5 μm, a very high thrust rigidity of about 1000 N / μm can be obtained. The radial rigidity is about 800 N / μm, which is a value sufficient for a rotating machine tool.
[0025]
Moreover, although the drive motor uses a thin one with a thickness of 35 mm, the outer diameter of the coil can be as large as 177 mmφ, so that a torque of 2 N · m or more can be secured at 3000 rpm. The encoder can be accommodated in the motor even if a commercially available product having an outer diameter of the detecting portion 5b of 70 mmφ and a thickness including the disc 5a of about 50 mm is used.
[0026]
With respect to the manufacture of the shaft body, it is not necessary to assemble the shaft body 1 from a plurality of parts as in the prior art, and a single part can be processed, so high processing accuracy can be easily obtained. As for the manufacture of the housing, the number of places where accuracy is required is reduced, so that processing and assembly are facilitated. As a result, it is possible to shorten the production time and the production cost with respect to the production of the entire rotating device.
[0027]
Further, since the shaft body 1 is short in the axial direction, the moment of inertia around the X axis is small, and the resonance frequency around the X axis can be about 1.5 times that of the conventional art. In the rotating device according to the present embodiment, this frequency can be set to about 1600 Hz, which is a sufficiently high frequency with respect to the machining disturbance. Therefore, the shaft body 1 resonates due to the machining disturbance and the machining accuracy such as the surface roughness of the workpiece is deteriorated. There is nothing.
[0028]
FIG. 2 is an enlarged view of the magnet unit 9. The ring-shaped magnets 9a and 9b having different polarities are concentrically arranged on the thrust housing 2a so that the magnetic circuit 10 in which the attractive force acts in the axial direction is formed. 9c is a magnetic yoke. By the way, there is no problem if the shaft body 1 is a magnetic body. However, in the case of a non-magnetic body such as ceramic, as shown in the figure, the ring-shaped magnetic body 1c is opposed to the magnets 9a and 9b. Arranged on the shaft body 1. In this embodiment, the magnetic body 1c is disposed on the shaft body 1 and the magnet 9 is disposed on the thrust housing 2a so as to face each other. However, the magnet 9 is disposed on the shaft body 1 and the magnetic body 1c is disposed on the thrust housing 2a. You may arrange | position so that it may mutually oppose.
[0029]
In order to obtain the attractive force in the axial direction, the magnet 9 does not have to be ring-shaped, but if the magnetic body 1c passes through a magnetic field that is not constant in the circumferential direction by rotating the shaft body 1, the fluctuation of the magnetic field is reduced. An eddy current flows through the shaft body 1 in the direction of cancellation, and heat is generated. Furthermore, since the eddy current flows in the magnetic field, a force is generated in a direction that suppresses or promotes the rotation of the shaft body 1, the rotational torque fluctuates, and rotation unevenness occurs. Therefore, as in the present embodiment, the magnet 9 is preferably ring-shaped.
[0030]
In addition, attraction force is generated even if the magnets do not have multiple polarities, but it is better to arrange magnets with opposite polarities in the radial direction and form a closed magnetic circuit in a limited space. It is desirable because it can increase power.
[0031]
FIG. 3 shows an example in which a rotating device is mounted on a slider and used as a vertical machine tool. Even if the work 7 is large, the load is not short because the slide bearing receives the weight vertically. Since the rotating device is thin, the distance from the slider 6a to the machining point of the workpiece 7 can be shortened, so the moment force on the slider 6a generated by the cutting force is small, the displacement and vibration of the workpiece 7 can be suppressed, and good shape accuracy・ Surface roughness can be obtained.
[0032]
In this embodiment, a permanent magnet is used as the attraction means, but an electromagnet or vacuum suction may be employed.
[0033]
By the way, in order to use it as an indexing board that requires a high rotational resolution at a low speed, not for the spindle of a machine tool as in the above embodiment, it is necessary to use an encoder disk with a large diameter in order to increase the resolution of the encoder. There is.
[0034]
In this case, as in the second embodiment shown in FIG. 4, a motor magnet 4b of a driving planar motor is disposed on the shaft body 1, and a motor coil 4a is disposed on the thrust housing 2a side facing the motor magnet 4b. The thrust housing 2a may be fixed to have a margin in the radial direction, and the encoder unit (encoder disk 5a and encoder detection unit 5b) may be disposed in this portion.
[0035]
Further, in the second embodiment shown in FIG. 4, a vacuum state is used for suction.
[0036]
That is, the clearance 12 between the thrust housing 2a and the shaft body 1 (including the encoder disk extension portion) is set to several μm, and the conductance of this portion is made extremely small to form a non-contact labyrinth seal. For this reason, air can be exhausted from the gap 12 between the shaft body 1 and the thrust housing 2a via the exhaust passage 11 connected to the vacuum pump, and this portion can be evacuated in a non-contact state. Since most of the inner part of the thrust bearing 3a can be used for vacuum suction, a relatively large suction force can be obtained.
[0037]
【The invention's effect】
As described above, according to the present invention, a very simple and thin rotating device can be realized. And since it is a simple structure, processing and assembly (production) costs can be reduced. Further, since the shaft body is thin, the resonance frequency in the lowest moment direction can be increased, and vibration of the shaft body due to machining disturbance can be suppressed. Furthermore, since the entire device can be made thin, when mounted on a machine tool, the overall size of the machine tool can be avoided, and the distance from the slider to the machining point can be reduced, so that the workpiece shape accuracy and surface roughness due to machining disturbances can be reduced. It is possible to suppress the deterioration of the thickness.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a first embodiment of a rotating device of the present invention.
2 is an enlarged view showing the principle of attraction by a magnet in FIG. 1. FIG.
FIG. 3 is a view showing a state in which the rotating device of the present invention is mounted on a machine tool.
FIG. 4 is a cross-sectional view of a second embodiment of the rotating device of the present invention.
FIG. 5 is a view showing a conventional rotating device mounted on a machine tool.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Shaft body 1a Thrust plate 1b Radial rotor 1c Magnetic body 2 Housing 2a Thrust housing 2b Radial housing 3a Thrust bearing 3b Radial bearing 4a Motor coil 4b Motor magnet 5a Encoder disk 5b Encoder detection part 6a Slide 6b Slide guide 7 Work 8 Byte 9 Magnet Portions 9a, 9b Ring-shaped magnet 9c Yoke 10 Magnetic circuit 11 Exhaust path 12 Gap 13 Rotating cylinder 14 Through hole

Claims (5)

In a rotating device comprising a housing, a hydrostatic bearing fixed to the housing, and a shaft body that is floatably supported by the hydrostatic bearing.
The shaft body is a disk-shaped, and radial support by a radial static pressure bearing which is fixed to the outer peripheral portion of the disk-shaped shaft body to said housing, a thrust hydrostatic the bottom surface of the disk-shaped shaft body fixed to the housing While supporting thrust by pressure bearings,
A suction means for sucking the disk-shaped shaft body in the axial direction , wherein a ring-shaped magnet and a ring-shaped magnet having a polarity opposite to that of the magnet are arranged in the radial direction on the housing or the disk-shaped shaft body. A rotating device comprising:   The rotating device according to claim 1, wherein a drive motor and a rotational position detector are accommodated in the housing.   The drive motor is composed of at least a motor magnet and a motor coil, the motor magnet and the motor coil are concentrically arranged, and the rotational position detector is on the shaft body center line, and is disposed in the drive motor. The rotating device according to claim 2, wherein the rotating device is accommodated in the rotating device.   3. The rotating device according to claim 2, wherein the driving motor includes a motor magnet disposed on a bottom surface of the shaft body, and a motor coil disposed at a position facing the motor magnet of the housing. The said housing is formed from the radial housing to which the radial bearing which supports the said radial support is fixed, and the thrust housing to which the thrust bearing which supports the said thrust is fixed. The rotating device as described.

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