JP2004324895A - Static pressure magnetic combined bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact static pressure magnetic combined bearing combining superior dynamic rigidity and high rotating accuracy of a static pressure gas bearing and superior static rigidity of a magnetic bearing, allowing the setting of the optimum bearing gap by designing the material quality of a rotor and actualizing higher accuracy and more compactness of the static pressure gas bearing and the magnetic bearing, no heating due to a reduction in core loss and higher speed rotation. <P>SOLUTION: The magnetic bearing and the static pressure gas bearing 9 having a restrictor 15 in a bearing stator 12 of the magnetic bearing are provided side by side for supporting the rotor 4 in non-contact. The magnetic bearing has a displacement measuring means for measuring the displacement of the rotor 4 and generates electromagnetic force in accordance with a measured value for the displacement measuring means. A laminated silicon steel plate is used for the rotor 4 and a ceramics coating layer 33 of a thickness of 1 mm or less is applied onto the laminated silicon steel plate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrostatic magnetic composite bearing in which a hydrostatic gas bearing and a magnetic bearing are combined, and for example, to a hydrostatic magnetic composite bearing used for a spindle device or the like of a high-speed cutting machine.

Magnetic bearings have a large bearing gap, so that the torque loss due to rotation is extremely small, and large static stiffness can be imparted by integral control.
FIG. 26 is a longitudinal sectional view showing a conventional high-speed milling magnetic bearing spindle device for aluminum material. This conventional spindle device has a touchdown bearing 251, a tool 252, a displacement sensor 253, a radial magnetic bearing 254, a thrust magnetic bearing 255, a motor 256, a radial magnetic bearing 257, a displacement sensor 258, and a main shaft 259. This magnetic bearing spindle device has various performances of a maximum rotation speed: 40,000 rpm, an output: 15 kW, and a maximum cutting capacity: 1250 cm ³ / min, and is very excellent for the above-mentioned applications.

  However, the magnetic bearing spindle device is easily affected by the natural frequency of bending of the spindle during machining, and therefore, it is necessary to configure a very complicated control system. Therefore, it is not suitable as a spindle device for a general-purpose machine tool which needs to cope with various processing conditions.

  On the other hand, non-contact bearings include static pressure gas bearings in addition to magnetic bearings. The hydrostatic gas bearing has extremely high rotational accuracy and excellent dynamic stability, but has a small static rigidity and a small load capacity due to its compressibility, and has almost no application to general-purpose machine tools.

  Therefore, as a spindle device for a high-speed processing machine, a composite bearing spindle device combining a hydrostatic gas bearing and a magnetic bearing as shown in a vertical sectional view in FIG. 27 has recently been proposed, and its practical use is being studied. This conventional spindle device includes a displacement sensor 263, a radial magnetic bearing 264, a thrust magnetic bearing 265, a motor 266, a radial magnetic bearing 267, a displacement sensor 268, a displacement sensor 270, a main shaft 271, and a hydrostatic gas bearing 272, 273. Have.

However, in the composite bearing spindle device shown in the figure, since the magnetic bearings 264 and 267 and the hydrostatic gas bearings 272 and 273 are arranged in the axial direction, the main shaft 271 becomes longer and the natural frequency of bending becomes lower. There is a problem that becomes. In addition, because the control system configuration is exactly the same as that of the spindle device that uses the magnetic bearing alone, the dynamic stability of the hydrostatic gas bearing is impaired, and it rather acts as a disturbance source. There are also problems.
Also, in order to obtain high rotational accuracy with this spindle device, a displacement sensor for a magnetic bearing is required to have high accuracy, but a displacement sensor used for a magnetic bearing is usually a magnetic sensor such as an eddy current sensor. Is used, and the resolution is about 1 μm. On the other hand, there is a capacitance type displacement sensor as a high precision displacement sensor, but it is expensive and difficult to use.
Therefore, at present, the objective of making up for the disadvantages while utilizing the features of the static pressure gas bearing and the magnetic bearing has not been sufficiently achieved.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and provide a hydrostatic magnetic composite bearing having excellent dynamic stiffness and high rotational accuracy of a hydrostatic gas bearing and excellent static stiffness of a magnetic bearing and capable of achieving compactness. It is to be.
Another object of the present invention is to make it possible to set an optimal bearing clearance by devising a material of the rotor, etc., to increase the accuracy of the hydrostatic gas bearing and the magnetic bearing, to make the bearing compact, to reduce heat loss by reducing iron loss, That is, high-speed rotation can be realized.

The hydrostatic magnetic composite bearing of the present invention has a displacement measuring means for measuring the displacement of the rotor, a magnetic bearing for generating an electromagnetic force in accordance with the measured value of the displacement measuring means, and a restrictor for the magnetic bearing. The rotor is provided in a non-contact manner by being provided with a hydrostatic gas bearing having the following. For this reason, it is possible to provide a bearing that takes advantage of both of the excellent dynamic rigidity and rotational accuracy of the static pressure gas bearing and the excellent static rigidity of the magnetic bearing. The hydrostatic gas bearing is, for example, a hydrostatic air bearing.
The hydrostatic magnetic composite bearing of the present invention may be a radial bearing or an axial bearing.
When the present invention is applied to a radial bearing, a separate bearing is not required for a main shaft serving as a rotor for support by static pressure and support by magnetism, so that a composite bearing that is short in the axial direction can be obtained, and the length of the main shaft can be reduced. As a result, the bending natural frequency is increased, and higher-speed rotation becomes possible. Further, the support center point of the magnetic bearing in the axial direction and the support center point of the hydrostatic gas bearing can be made substantially coincident, and control of both bearings is facilitated.
When applied to an axial bearing, the configuration is more compact and the diameter of the bearing-facing surface of the rotor can be reduced as compared with a case where the hydrostatic gas bearing and the magnetic bearing are simply arranged side by side in the radial direction.

According to a first aspect of the present invention, the rotor comprises a laminated silicon steel sheet, and a ceramic coating layer having a thickness of 1 mm or less is formed on the laminated silicon steel sheet.
By configuring the rotor with a laminated silicon steel sheet, iron loss during high-speed rotation can be reduced, and heat generation of the rotor during high-speed rotation can be suppressed. Further, by coating the outer diameter with a ceramic material, even when the bearing surface comes into contact with the rotor, damage to the rotor can be minimized. When the coating layer is made of ceramics, it can be applied to high-speed rotation without causing iron loss due to magnetic flux from the electromagnet of the magnetic bearing. Furthermore, the outer peripheral surface of the coating layer is the rotor surface of the hydrostatic gas bearing, and the inner peripheral surface is the rotor surface of the magnetic bearing.By adjusting the thickness of the coating layer, the optimal bearing gap of the hydrostatic gas bearing can be adjusted. The bearing clearance of the magnetic bearing can be set.

  According to a second aspect of the present invention, there is provided a hydrostatic magnetic composite bearing wherein the rotor is made of a soft magnetic solid material having low thermal expansion and a ceramic coating layer having a thickness of 1 mm or less is provided on the solid material. When the rotor is provided on the main shaft, the main shaft is also preferably made of a solid material of the same material as the rotor. As the solid material, for example, an invar material can be used. As described above, by using a material that is solid for the rotor, the natural frequency of bending of the rotor can be increased, and the rotor can be rotated to a higher speed. Further, even when the rotor generates heat, the change in the bearing gap is small due to the low thermal expansion, so that stable static pressure gas bearing performance can be secured. Further, since the amount of expansion in the axial direction is small, it is effective in improving machining accuracy when used in a machine tool spindle.

Since the hydrostatic magnetic composite bearing and the spindle device of the present invention are each a combination of the hydrostatic gas bearing and the magnetic bearing in a predetermined relationship, the dynamic dynamic rigidity of the hydrostatic gas bearing and the magnetic bearing are excellent. The structure becomes compact while having both static rigidity. When applied to a radial bearing, the spindle length can also be reduced.
In addition, it is possible to set the optimal bearing clearance by devising the material of the rotor, etc., to realize high precision, compactness, prevention of heat generation by reducing iron loss, high speed rotation, etc. of the hydrostatic gas bearing and magnetic bearing. it can.

A first proposal example on which the present invention is based will be described with reference to FIGS.
FIG. 1 is a longitudinal sectional view of a spindle device to which the hydrostatic magnetic composite bearing according to the proposed example is applied. This hydrostatic magnetic composite bearing spindle device 1 is a spindle device of a built-in motor type of a machine tool, and includes a pair of hydrostatic magnetic composite bearings disposed before and after a motor 5 in a cylindrical housing 2 serving as a spindle mount. The main shaft 4 is rotatably supported via bearings 3 and 3 and a thrust magnetic bearing 10 at the rear end. The main shaft 4 serves as a rotor of the hydrostatic composite bearing 3. The motor 5 is composed of a motor rotor 6 provided integrally with the main shaft 4 and a stator 7 provided directly on the housing 2.
Flanges 21A and 21B are formed at the front and rear ends of the housing 2, and inner peripheral surfaces of the flanges 21A and 21B are formed as protective bearing surfaces 22 made of a material having excellent lubricity. Thereby, even if an abnormality occurs in the composite bearing 3 and the main shaft 4 touches down, seizure of the main shaft 4 is prevented.
The thrust magnetic bearing 10 includes a bearing rotor 19 provided integrally with the main shaft 4 and a pair of bearing stators 20A and 20B installed in the housing 2 and sandwiching the bearing rotor 19 from front and rear in the axial direction. The coil current of the bearing stators 20A and 20B is controlled by a measurement value of a thrust displacement sensor 24 that detects an axial displacement of the main shaft 4. The thrust displacement sensor 24 is provided on the rear wall 23 of the housing 2.

  The front and rear static pressure magnetic composite bearings 3 and 3 are obtained by integrating a radial magnetic bearing 8 and a radial static pressure gas bearing 9 so as to form a shared part in the components as follows. A static pressure air bearing is used for the static pressure gas bearing 9. In each of the embodiments and proposals described below, a hydrostatic air bearing is used for each hydrostatic gas bearing. The radial magnetic bearing 8 includes a magnetic bearing rotor 11 provided on the outer periphery of the main shaft 4 and a bearing stator 12 installed in the housing 2. The bearing stator 12 is formed in a ring shape by a core 13, a coil 14, and a coil covering member 18. For the core 13, a soft magnetic solid material having a large specific resistance is used. As shown in FIG. 2, the core 13 is formed by projecting a plurality of yoke portions 13a radially outward from a ring-shaped portion, and the coil 14 is wound around each yoke portion 13a. The gap between the adjacent yoke portions 13a, 13a is filled by a resin mold, or by thermal spraying made of a non-magnetic metal material or a ceramic material, or by a core covering material 18 made of a partition made of a non-magnetic metal material or a ceramic material. Is done. The inner diameter surface of the core covering member 18 is finished to the same cylindrical surface together with the distal end surface of the yoke portion 13a. The core covering member 18 and the yoke portion 13a form a cylindrical inner diameter surface of the bearing stator 12.

Inside the ring-shaped portion of the bearing stator core 13, an air supply passage 16 is formed over the entire circumference, and the throttle 15 branching off from the air supply passage 16 and supplying air to the bearing gap is formed by the electromagnetic force of each yoke portion 13 a. The opening is provided on the inner diameter surface of the tip, which is the generation surface. The air supply passage 16 is connected to a supply source (not shown) of compressed air as a pressurized fluid by a pipe or the like from an air supply port 17 provided at one or a plurality of positions in a circumferential direction. The compressed air is jetted into a bearing gap d formed between the inner diameter surface of the bearing stator 12 and the main shaft 4.
The radial static pressure gas bearing 9 is constituted by the throttle 15, the bearing stator core 13 and the core covering member 18 which also serves as a bearing gap forming member. The bearing stator core 13 also serves as a member forming the throttle 15 and the air supply passage 16.
With this configuration, the hydrostatic gas bearing 9 is disposed within the entire axial width of the magnetic bearing 8. Since the gap of the magnetic bearing 8 is a gap between the bearing stator core 13 and the main shaft 4, the bearing gap d of the hydrostatic gas bearing 9 and the gap of the magnetic bearing 8 are mutually different in the axial direction of the main shaft 4. It will be provided in the same position.
As shown in FIG. 3, the throttle 15 is a self-generated throttle, and includes an air supply hole 15 a provided in the core 13 and a bearing gap d. The air supply hole 15a has a stepped inner diameter, and a portion that opens to the hydrostatic gas bearing surface formed by the inner surface of the core 13 is a fine hole, and the diameter of the fine hole portion is 1 mm or less. . As described above, when the self-contained throttle is used as the air supply type of the static pressure gas bearing, stability against a pneumatic hammer is improved, and shaft stability in a high frequency range, that is, dynamic rigidity can be increased. It is preferable that the apertures 15 are arranged at at least three places in the circumferential direction of the main shaft 4.

  In this proposed example, the whole yoke portion 13a is made of a material which is peeled off. However, as shown in FIG. 4, only the diaphragm peripheral portion 13aa of the yoke portion 13a is made of a material which is peeled off. A certain non-narrowing portion 13ab may be a laminated silicon steel sheet. In any case, since the part of the autonomous drawing 15 formed by the fine holes is made of a peeled material, compared with the case where the core is made of a laminated steel sheet which is usually used, such a small hole is formed. The formation can be easily performed, and the hydrostatic gas bearing can be formed with high accuracy. In addition, as in the example of FIG. 4, when the laminated silicon steel sheet is used for portions other than the drawing peripheral portion 13aa, the iron loss generated in the core 13 can be reduced as compared with the case where all the members are made of solid material.

Since the hydrostatic magnetic composite bearing 3 combines the hydrostatic gas bearing 9 and the magnetic bearing 8 in this manner, the dynamic dynamic rigidity and the rotational accuracy of the hydrostatic gas bearing 9 and the magnetic bearing 8 are excellent. A bearing that makes use of both features of static rigidity can be obtained.
In addition, since the static pressure gas bearing 9 and the magnetic bearing 8 also serve as components, the configuration becomes compact as compared with a case where the static pressure gas bearing and the magnetic bearing are simply arranged side by side in the axial direction. The length of the main shaft 4 can be reduced. As a result, the bending natural frequency is increased, and higher-speed rotation becomes possible. In particular, in this proposed example, the bearing stator core 13 and the core covering member 18 of the magnetic bearing 8 also serve as a bearing gap forming member of the hydrostatic gas bearing 9, and the bearing stator core 13 is a member forming the throttle 15 and the air supply passage 16. Therefore, the components are highly shared, and the effect of making the configuration compact is high.

  A control system of the static pressure magnetic composite bearing 3 will be described. The bearing stator 12 is provided with pressure detection vents 26 which penetrate the core covering member 18 in the radial direction and open to the bearing gap d at four circumferential positions near the throttle 15 at equal intervals. Pressure sensors 27A to 27D are provided in the sensor mounting holes 25 communicating with each other. Each of the pressure sensors 27A to 27D is a differential pressure type air microsensor that detects a radial displacement of the main shaft 4 as a set of two sensors that are diametrically opposed to each other. That is, the pressure sensors 27A and 27B diametrically opposed to each other form one set, the pressure sensors 27C and 27D form another set, and one of the pressure sensors 27A and 27B has a corresponding vent. The pressure difference at the hydrostatic gas bearing surface where the opening 26 opens is measured, and this is converted into the displacement of the main shaft 4 in the Y-axis direction. Also, between the other pair of pressure sensors 27C and 27D, the pressure difference on the hydrostatic gas bearing surface where the corresponding vent hole 26 is opened is measured, and this is converted into the displacement of the main shaft 4 in the X-axis direction.

The magnetic bearing control means 28 including the controller 28a and the amplifier 29 has a feedback control system in the Y-axis direction and the X-axis direction. In the feedback control system in the Y-axis direction, the pressure sensors 27A and 27B are used. Based on the detected displacement of the main shaft 4 in the Y-axis direction, feedback control of the magnetic bearing 8 in the Y-axis direction is performed. That is, in accordance with the displacement of the main shaft 4, the current supplied to the coil 14 at a position corresponding to the pressure sensors 27A and 27B or some of the coils 14 in the vicinity thereof via the amplifier 29 is adjusted so that the main shaft 4 moves in the Y-axis direction. Control so that there is no bias. That is, control is performed so that the spindle 4 coincides with the target position. Similarly, the feedback control system in the X-axis direction of the magnetic bearing control unit 28 controls a predetermined current of the coil 14 based on the measured values of the other pressure sensors 27C and 27D.
As described above, since the air microsensor system using the pressure sensors 27A to 27D for detecting the static pressure in the bearing gap d is used as the displacement sensor of the magnetic bearing 8, the zero point (the target value) of the control system of the magnetic bearing 8 is set. ) And the support center point (pressure equilibrium point) of the static pressure gas bearing 9 can be easily matched, and complicated sensor adjustment is not required. In addition, uneven magnetic characteristics and roundness errors on the target surface of the rotor sensor, which are problems with other types of sensors, are irrelevant.

The feedback control by the magnetic bearing control means 28 is only an integral operation or a proportional integral operation, and no compensation at a high frequency is performed. Further, when the zero point of the magnetic bearing control system and the support center point of the static pressure gas bearing 9 deviate due to drift of the pressure sensors 27A and 27B, a slight dead zone w (FIG. 5) may be provided in the integral control. The dead zone w can be set by providing a dead zone circuit 31 between the pressure sensors 27A, 27B and the magnetic bearing control unit 28 as shown in FIG. 6, or the dead zone can be set in the control circuit constituting the magnetic bearing control unit 28. The setting may be made by providing a circuit. By providing the dead zone w in this manner, malfunction of the magnetic bearing 8 due to temperature drift or the like can be suppressed. That is, the dynamic stiffness (high-frequency range) is shared by the static pressure gas bearing 9 and the static stiffness (low-frequency range) is shared by the magnetic bearing 8 so that the bearings can be reliably shared. It can be used to avoid interference with each other. Further, as described above, since the magnetic bearing 8 has a low frequency control system of an integral operation or a proportional integral operation, the pressure sensors 27A to 27D having relatively slow response can be used as displacement sensors.
The performance of the magnetic bearing 8 can be set by the setting of the magnetic bearing control means 28. In general, in the case of a magnetic bearing, it is difficult to effectively generate a damping force in a high frequency range and to stably float the main shaft. There's a problem. Therefore, in the present invention, the magnetic bearing 8 is used only for the purpose of enhancing the bearing rigidity in a low frequency range, which is a feature of the magnetic bearing 8.

As the amplifier 29 for supplying a current to the coil 14 of the magnetic bearing 8, a circuit having a linearization circuit for linearizing the current-electromagnetic force, for example, a current square feedback circuit is used. Thereby, linearization can be performed without flowing a bias current, and negative rigidity peculiar to a magnetic bearing does not occur. That is, generation of negative rigidity in the magnetic bearing 8 can be avoided, and the stability of the hydrostatic gas bearing 9 can be prevented from being impaired by the negative rigidity. In addition, iron loss in the main shaft 4 caused by the bias current when the main shaft 4 rotates can be eliminated, and high-speed rotation can be performed.
A band elimination filter 32 (FIG. 7) synchronized with the rotation speed of the main shaft 4 may be inserted into the magnetic bearing control unit 28. As a result, the electromagnetic force from the electromagnet of the magnetic bearing 8 does not act on the run-out due to the rotor imbalance when the main shaft 4 rotates. As described above, when the magnetic bearing control means 28 is configured by an integral operation, the acting force of the magnetic bearing 8 in the high frequency range acts on the main shaft 4 as an unstable force. When the main shaft 4 rotates, the runout of the main shaft 4 mainly includes a rotation synchronization component. By selectively removing this, the main shaft 4 can be rotated stably.

In this proposed example, the displacement of the main shaft 4 is directly detected by the pressure sensors 27A to 27D. However, the displacement between the main shaft 4 and the hydrostatic gas bearing surface is converted from the value measured by the pressure sensor. May be determined, and control by the magnetic bearing control unit 28 may be performed according to the change in the gap.
Instead of disposing the pressure sensor inside the core 13 of the magnetic bearing 8 as described above, a hollow pipe (not shown) is arranged so as to communicate with the bearing gap of the hydrostatic gas bearing 9, and an external pressure The pressure may be measured by a sensor. When the bearing size is small and there is a space for accommodating the pressure sensor outside, it is preferable to arrange the pressure sensor outside.
Further, as shown in FIG. 8, a pressure sensor 27 is disposed directly on the inner diameter portion of the magnetic bearing 8, for example, on a portion such as the core covering member 18, and measures the pressure between the main shaft 4 and the core 13 to displace the main shaft 4. You may make it convert to.

9 and 10 show a hydrostatic magnetic composite bearing according to another proposed example. In this example, an electromagnet of the radial magnetic bearing 8 is used in a hydrostatic magnetic composite bearing 3A in which a throttle 15 for supplying air to a bearing gap d of a hydrostatic gas bearing 9A is formed in a core 13A of a bearing stator 12 of the radial magnetic bearing 8A. Has a so-called horseshoe shape, and a pair of magnetic poles 13Aa, 13Aa are arranged in the axial direction of the main shaft 4. The polarity of each magnetic pole 13Aa on the same circumference is the same. By doing so, it is possible to reduce iron loss generated in the main shaft 4 as the main shaft 4 rotates. Other configurations and effects are the same as those of the first proposed example. The number of cores 13A, in other words, the number of electromagnets is preferably three or more in the circumferential direction.
As described above, the magnetic bearing 8A has three or more electromagnets, the magnetic poles 13Aa of the core 13A of each electromagnet are arranged in the rotation axis direction, and the polarities of the magnetic poles 13Aa on the same circumference are matched. In addition, the hysteresis loss and the eddy current loss generated in the main shaft portion of the magnetic bearing 8A with the rotation of the main shaft 4 can be reduced. In addition, since heat generation of the main shaft 4 due to these losses can be suppressed, reduction of the bearing gap due to thermal expansion of the main shaft 4 can be minimized, and stable performance of the static pressure gas bearing 9A can be obtained.

  The bearing 3B of FIGS. 11 to 13 is obtained by improving the core shape of the radial magnetic bearing 8A with respect to the examples of FIGS. Of the yokes 13Ba, 13Bb of the core 13B arranged in the axial direction of the main shaft 4, one yoke 13Ba side is shared with the yoke adjacent in the circumferential direction to simplify the shape. By configuring the electromagnet in this manner, the number of steps for processing the yoke 13 </ b> B of the electromagnet can be reduced, the workability can be improved, and the iron loss in the magnetic bearing main shaft portion generated with the rotation of the main shaft 4 can be further reduced. It can be reduced and can cope with higher speed rotation.

FIG. 14 shows a first embodiment of the present invention. In this embodiment, a ceramic coating layer 33 is applied to the surface of the main shaft 4 facing the bearing 3 in the first proposal example described above. Thereby, seizure of the main shaft 4 and the bearing surface at the time of touchdown can be prevented. Further, since the coating layer 33 is made of ceramics, when the main shaft 4 rotates during the operation of the magnetic bearing 8, it is possible to suppress the occurrence of iron loss inside the main shaft 4 and to cope with high-speed rotation of the main shaft 4. . Further, the outer peripheral surface of the coating layer 33 is the rotor surface of the static pressure gas bearing 9 and the inner peripheral surface is the rotor surface of the magnetic bearing 8. By adjusting the thickness of the magnetic bearing 8, an optimal gap between the static pressure gas bearing 9 and the magnetic bearing 8 can be set. By limiting the thickness of the coating layer 33 to 1 mm or less to increase the magnetic bearing gap d ', a desired electromagnetic force can be generated without increasing the current supplied to the coil 14.
Further, a laminated silicon steel plate (not shown) may be used for the rotor part of the magnetic bearing 8 of the main shaft 4, and the ceramic coating layer 33 may be applied thereon. The rotor section made of the laminated silicon steel sheet is provided, for example, on the outer periphery of the main shaft 4. In that case, the use of the laminated silicon steel sheet can further reduce the iron loss during high-speed rotation and suppress the heat generation of the rotor during high-speed rotation.
It is preferable to use a low-thermal-expansion soft magnetic material, for example, an invar material, for the material of the main shaft 4 or the material of the rotor provided on the outer periphery thereof as described above, and to apply a ceramic coating layer 33 on the outer peripheral surface thereof. As a result, the bending natural frequency of the main shaft 4 or the rotor is increased, and it is possible to rotate to a higher speed. Further, since the invar material has a low coefficient of thermal expansion, even if the temperature of the main shaft 4 rises, the amount of decrease in the bearing gap d ′ due to the thermal expansion of the main shaft 4 can be suppressed to a small value, and the invar material is suitable for the magnetic bearing 8. Has magnetic properties. For this reason, stable static pressure gas bearing performance can be secured. In addition, since the amount of expansion in the axial direction is small, when applied to a spindle device for a machine tool, it is effective in improving machining accuracy. Further, since ceramics generally have a low coefficient of thermal expansion, when the ceramic coating layer 33 is applied on the main shaft 4 made of, for example, ferritic stainless steel, the ceramic coating layer 33 is cracked due to a difference in the coefficient of thermal expansion of the main shaft 4. However, such a problem can be solved by using an invar material.

In the above-described embodiments and proposals of the hydrostatic magnetic composite radial bearing, the throttle 15 is provided on the bearing stator core 13. However, the throttle 15 may be formed on the coil covering member 18 or the like, avoiding the core 13.
Further, in the above-described embodiments and proposals of the hydrostatic magnetic composite radial bearing, the magnetic bearing 8 and the hydrostatic gas bearing 9 are used as parts, but the magnetic bearing and the hydrostatic gas bearing are not necessarily used as parts. The static pressure gas bearing may be provided within the entire axial width of the magnetic bearing, or the magnetic bearing may be provided within the entire axial width of the static pressure gas bearing. Alternatively, the bearing gap d of the hydrostatic gas bearing and the gap between the shaft of the magnetic bearing and the stator core may be provided at substantially the same position in the axial direction. The configuration in which the widths of the magnetic bearing and the hydrostatic bearing have a common part without sharing the parts is to make the arrangement of the parts constituting the magnetic bearing and the parts forming the hydrostatic bearing different in the circumferential direction. Etc. are realized.

  FIG. 15 shows an example in which this hydrostatic composite bearing is applied to an axial bearing. This hydrostatic / magnetic composite axial bearing device is configured such that a bearing rotor 41a, which is a flange-shaped thrust support portion of a main shaft 41 made of a magnetic material, is sandwiched between two hydrostatic / magnetic composite axial bearing portions 42 and 43 from both axial sides. You. Each of the static pressure magnetic composite axial bearings 42 and 43 accommodates coils 46 and 47 in cores 44 and 45 of an electromagnet, and has a throttle 48 provided in the cores 44 and 45. It is provided in a ring shape. The restrictor 48 is a self-contained restrictor, and is composed of an air supply hole 48a having a fine hole at the tip end, which opens to the bearing surfaces of the cores 44 and 45, and bearing gaps d1 and d2. The cores 44 and 45 and the coils 46 and 47 constitute a bearing stator 52 of an axial magnetic bearing 49, and the cores 44 and 45 and the throttle 48 constitute an axial hydrostatic gas bearing 50.

  By ejecting the pressure fluid between the cores 44, 45 and the rotor 41a, pressure is generated between the cores 44, 45 and the rotor 41a. In addition, the provision of the self-contained throttle 48 automatically changes the pressure and the gap between the cores 44 and 45 and the gaps d1 and d2 between the rotor 41a and the static pressure gas having an automatic centering function. A bearing can be formed. Thus, the rotor 41a can be stably levitated. In this case, by minimizing the gaps d1 and d2 between the cores 44 and 45 and the rotor 41a to 0.1 mm or less, the bearing rigidity of the hydrostatic gas bearing is increased, and the rotor 41a is stable even with the hydrostatic gas bearing alone. And can surface.

  This static pressure magnetic composite bearing is provided with a displacement sensor 51 for measuring the distance between the cores 44 and 45 and the rotor 41a, and the current flowing through the coils 46 and 47 is feedback controlled according to the measured value of the displacement sensor 51. Magnetic bearing control means 53 is provided. The magnetic bearing control means 53 controls the current through, for example, an amplifier 54. As a result, a bearing configuration that serves both as a static pressure gas bearing and a magnetic bearing is made possible. As the magnetic bearing control means 53, one having the same function as the magnetic bearing control means 28 described in the first proposal example or the like can be used.

  In the hydrostatic magnetic composite axial bearing device of this example, instead of providing the displacement sensor 51, the pressure of the hydrostatic gas bearing surface is measured, and this pressure is used to measure the bearing gap d in the hydrostatic gas bearing 50, that is, the core 45 of the electromagnet. It may be obtained by converting the size of the gap d (d1, d2) between the rotor and the rotor 41a. The current of the coils 46 and 47 is controlled by the magnetic bearing control means 53 based on the detection result of the size of the gap d. In the case of displacement measurement by pressure measurement, high-precision sensing is possible without malfunction of the sensor due to uneven magnetic characteristics of the target surface of the rotor sensor, which is a problem with other types of sensors.

For this pressure measurement, in this example, as shown in FIG. 16, a pressure sensor 55 is disposed inside the cores 44 and 45 of the electromagnet, and the pressure of the hydrostatic gas bearing 50 is directly measured. good.
As shown in FIG. 17, a hollow pipe 56 may be provided directly connected to the static pressure gas bearing 50, and the pressure may be measured by an external pressure sensor 57. In this case, a fine hole 59 for pressure measurement is provided in a component on the bearing surface of the hydrostatic gas bearing 50 such as the core 44, and a hollow pipe 56 is connected to the fine hole 59. If the bearing size is small and there is space for the pressure sensor outside, it is advantageous to provide the pressure sensor 57 outside. Further, by regulating the diameter of the fine hole 59 provided for pressure measurement to 1 mm or less, the influence on the hydrostatic gas bearing is reduced, and the inner diameter (diameter) of the pipe 56 connected thereto is also regulated to 1 mm or less. By doing so, it is possible to measure the pressure without lowering the frequency characteristics.

  FIG. 18 is a diagram showing a cross section taken along line AA of FIG. In this example, the sensor pressure measurement points are set to three or more equal pitches (three measurement points a1, a2, and a3 in FIG. 18) on the same circumference on the hydrostatic gas bearing surface of the hydrostatic magnetic composite axial bearing. The values of the gaps d1, d2 between the rotor 41a of each part and the electromagnet cores 44, 45 are converted from the measured values, and the values are averaged. Thus, the axial position of the rotor 41a can be accurately measured. The calculation for taking the average is performed by, for example, the magnetic bearing control unit 53.

  Instead of measuring the pressure at three locations as described above, the pressure may be measured at two opposed measurement points b1 and b2 180 ° apart on the circumference as shown in FIG. FIG. 19 is a diagram corresponding to the AA cross section of FIG. By setting the pressure measurement points b1 and b2 at two points 180 ° apart on the circumference in this way, the rotor 41a is not affected by the pitching motion or the yawing motion of the rotor 41a and the number of pressure sensors is minimized. Axial position can be measured.

When the hydrostatic magnetic composite axial bearings 42 and 43 are provided opposite to both sides of the rotor 41a as in the example of FIG. 16, the measurement points for measuring the pressure in the bearing gaps d1 and d2 are as shown in FIG. Each bearing gap d1, d2 may be provided at one location. In this case, the measurement point c1 of one bearing gap d1 and the measurement point c2 of the other bearing gap d2 are two points 180 ° apart on the same circumference on the projection plane. The magnetic bearing control means 53 calculates the difference between the bearing gaps d1 and d2 obtained from the pressure measurement values at the two measurement points c1 and c2, and performs current control. Accordingly, the axial position of the rotor 41a can be measured with the minimum number of pressure sensors even when the rotor 41a is thermally expanded without being affected by the pitching motion or the yawing motion of the rotor 41a.
By the method described with reference to FIGS. 18 to 20, the axial displacement of the rotor 41a can be measured accurately and at low cost.

  The pressure sensors shown in the embodiments and the proposals, for example, the pressure sensors 51, 55, and 27 of the examples of FIGS. 15 and 16 and the example of FIG. 8 may use semiconductor pressure sensors. This makes it possible to make the apparatus compact and to take out the measurement results directly to the outside by an electric signal.

FIG. 21 shows a hydrostatic magnetic composite axial bearing according to still another proposed example. In this example, an axial bearing that supports only one of the rotors 41a of the main shaft 41 is used. That is, the stator core 45 of the magnetic bearing 49 and the throttle 48 of the static pressure gas bearing 50 are arranged only on one side in the axial direction of the rotor 41a.
In this example, the acting force Fm of the magnetic bearing 49 on the rotor 41a acts as an attraction force, while the acting force Fs of the static pressure gas bearing 50 on the rotor 41a acts as a repulsive force. Therefore, the rotor cannot be supported when the axial direction of the rotor is in the vertical direction by itself using the static pressure gas bearing 50. However, by combining with the magnetic bearing 49, the rotor 41a can be supported irrespective of the bearing installation direction. As described above, the magnetic bearing 49 and the hydrostatic gas bearing 50 are arranged only on one of the thrust support portions 41a of the main shaft 41, and the hydrostatic magnetic composite bearing is configured to balance the attractive force and the repulsive force. The bearing configuration becomes more compact.

FIG. 22 is a longitudinal sectional view of a hydrostatic magnetic composite bearing spindle device according to another application example. This hydrostatic magnetic composite bearing spindle device 1 differs from the hydrostatic magnetic composite bearing spindle device 1 of FIG. 1 in the arrangement of the motor 5 and the bearings 3, 3, and 10. Is located at the end of The thrust magnetic bearing 10 is disposed between the front and rear hydrostatic magnetic composite bearings 3, 3. Other configurations are the same as those of the above-mentioned proposal.
In the motor arrangement of the example of FIG. 1, when the motor 5 is set to a high output, the thickness and the mass of the rotor 6 of the motor 5 may be increased to lower the bending natural frequency, but as shown in the example of FIG. This can be dealt with by disposing the motor 5 at the rear end of the main shaft 4.

  FIG. 23 shows still another application example. This hydrostatic magnetic composite bearing spindle device 1 uses an eddy current type displacement sensor 30 as a sensor for detecting a radial displacement of the main shaft 4 with respect to the bearing in the hydrostatic magnetic composite bearing spindle device 1 of FIG. . The position of the sensor 30 with respect to each of the hydrostatic magnetic composite bearings 3 may be either before or after. However, in the illustrated example, the position with respect to the front hydrostatic magnetic composite bearing 3 is the front of the bearing, and the rear hydrostatic magnetic composite bearing is provided. The one for 3 is the rear of the bearing. Note that, instead of the eddy current displacement sensor 30, a reluctance displacement sensor or a capacitance displacement sensor may be used. The other configuration is the same as the proposed example of FIG.

FIG. 24 shows still another spindle device constituted by a hydrostatic magnetic composite bearing. This spindle device includes two sets of hydrostatic magnetic composite radial bearings 65 and 66, one set of hydrostatic magnetic composite axial bearing 67, and a motor 69 for rotating a main shaft 68. The main shaft 68 has a flange-shaped rotor 41 a supported by a hydrostatic magnetic composite axial bearing 67. Any of the static pressure / magnetic composite radial bearings 65 and 66 and the static pressure / magnetic composite axial bearing 67 described in each of the above-described embodiments or the proposed examples may be used.
Also, in the spindle device shown in the figure, two sets of hydrostatic magnetic composite radial bearings 65 and 66 are provided, as shown in FIG. Bearings 65A and 66A may be used. Other configurations of the hydrostatic composite bearing spindle device of FIG. 25 are the same as those of the spindle device shown in FIG.
In the spindle devices of these examples, it is not always necessary to configure all bearings with a hydrostatic composite bearing. When it is necessary to increase the static rigidity only in the thrust direction, only the axial bearing portion may be constituted by a hydrostatic magnetic composite bearing, and the bearing support in the radial direction may be constituted by a hydrostatic gas bearing. When it is necessary to increase the static rigidity only in the radial direction, a hydrostatic magnetic composite radial bearing 65 may be arranged at the end on the spindle load side, and the other bearing support may be constituted by a hydrostatic gas bearing. .

1 is a longitudinal sectional view of a spindle device to which a hydrostatic magnetic composite bearing according to a first proposal example as a basis of the present invention is applied. FIG. 3 is an explanatory diagram showing a combination of a cross-sectional view of the hydrostatic magnetic composite radial bearing and a block diagram of a bearing control system. It is the elements on larger scale of the static pressure magnetic composite radial bearing. It is the elements on larger scale of the modification of the yoke part of the static pressure magnetic composite radial bearing. It is explanatory drawing which shows the example of current control of the static pressure magnetic composite radial bearing. It is a block diagram which shows the modification of the control system of the static pressure magnetic composite radial bearing. It is a block diagram showing another modification of the control system of the same static pressure magnetic composite radial bearing. It is sectional drawing of the hydrostatic composite radial bearing which concerns on another proposal example. It is a cross-sectional view of a hydrostatic magnetic composite radial bearing according to yet another proposed example. It is the longitudinal section. It is a longitudinal cross-sectional view of the hydrostatic magnetic composite radial bearing concerning another proposal example. FIG. 12 is a sectional view taken along line XII-XII of FIG. 11. FIG. 12 is a sectional view taken along line XII1-XII1 of FIG. 11. FIG. 1 is a partial cross-sectional view of a hydrostatic magnetic composite radial bearing according to a first embodiment of the present invention. It is an explanatory view showing a partial sectional view of a hydrostatic magnetic composite axial bearing according to still another proposed example in combination with a block diagram of a bearing control system. It is an explanatory view showing a partial sectional view of a hydrostatic magnetic composite axial bearing according to still another proposed example in combination with a block diagram of a bearing control system. FIG. 11 is a partial cross-sectional view of a hydrostatic magnetic composite radial bearing according to still another proposed example. It is an explanatory view of the measurement point. It is explanatory drawing of another example of the measurement point. (A), (B) is an explanatory view of another example of each measurement point. FIG. 11 is a partial cross-sectional view of a hydrostatic magnetic composite radial bearing according to still another proposed example. FIG. 11 is a longitudinal sectional view of a hydrostatic magnetic composite bearing spindle device according to another application example on which the present invention is based. FIG. 13 is a longitudinal sectional view of a hydrostatic magnetic composite bearing spindle device according to still another application example. FIG. 13 is a longitudinal sectional view of a hydrostatic magnetic composite bearing spindle device according to still another application example. FIG. 13 is a longitudinal sectional view of a hydrostatic magnetic composite bearing spindle device according to still another application example. It is a longitudinal section of the conventional example. It is a longitudinal section of other conventional examples.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Hydrostatic composite bearing spindle device 2 ... Housing 3 ... Hydrostatic composite bearing 4 ... Spindle (rotor)
8 Radial magnetic bearing 9 Radial static pressure gas bearing 10 Thrust magnetic bearing 12 Bearing stator 13 Stator core 14 Coil 15 Throttle 15a Air supply holes 27A to 27D Pressure sensors (displacement detecting means)
28 ... magnetic bearing control means 33 ... coating layer 41 ... spindle (rotor)
41a rotor 44, 45 stator core 46 coil 48 throttle 49 magnetic bearing 50 hydrostatic gas bearing 53 magnetic bearing control means 51 displacement sensor 52 bearing stator 55 pressure sensor d bearing clearance

Claims (2)

By having a displacement measuring means for measuring the displacement of the rotor, a magnetic bearing for generating an electromagnetic force according to the measured value of the displacement measuring means, and a hydrostatic gas bearing having a throttle in the bearing stator of the magnetic bearing, A hydrostatic magnetic composite bearing in which the rotor is supported in a non-contact manner, a laminated silicon steel sheet is used for the rotor, and a ceramic coating layer having a thickness of 1 mm or less is provided on the laminated silicon steel sheet. It has displacement measuring means for measuring the displacement of the rotor, and a magnetic bearing which generates an electromagnetic force according to the measured value of the displacement measuring means, and a hydrostatic gas bearing having a throttle in a bearing stator of the magnetic bearing are provided side by side. A hydrostatic composite bearing comprising a non-contact support for the rotor, a soft magnetic material having a low thermal expansion, and a ceramic coating layer having a thickness of 1 mm or less provided on the material.

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