JPH11254205A - Main spindle supporting method and main spindle head of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a main spindle with a certain mobile rigidity even in the low speed area by supporting the main spindle with a magnetic bearing. SOLUTION: With regard to the method of supporting a main spindle 1 of a machine tool in a rotatable manner, the means of supporting the main spindle 1 is changed according to the number of revolutions so as to support it with a thrust magnetic bearing 30 and radial magnetic bearings 10, 20 in case the number of revolutions of the main spindle 1 is more than a certain number and to support it with the thrust magnetic bearing 30, the radial magnetic bearings 10, 20 and an angular ball bearing 3 in case the number of revolutions of the main spindle 1 is less than a certain number. In full revolution area of the main spindle 1, the mobile rigidity of a spindle head can be made higher than the rigidity required for actual cutting therefore all machining can be performed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supporting a main shaft of a machine tool by a magnetic bearing, and a main shaft head of the machine tool having a main shaft supported by a magnetic bearing.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional spindle head used in a machine tool, in which the spindle is supported by magnetic bearings. FIG. 1 shows a spindle head used in a vertical machine tool as an example.

As shown in FIG. 1, the spindle head includes a spindle 1 whose axial direction is oriented vertically, and a rear radial magnetic bearing 10 that supports the rear side (upper side) of the spindle 1 in the radial direction. A front radial magnetic bearing 20, which also supports the front side (lower side) of the main shaft 1 in the radial direction, and a rear radial magnetic bearing 10, a front radial magnetic bearing 2;
0, a thrust magnetic bearing 30 for supporting the main shaft 1 in the axial direction, and a rear radial magnetic bearing 1
0, front radial magnetic bearing 20 and thrust magnetic bearing 3
0, and a rear angular contact ball bearing 2 provided on the rear side of the rear radial magnetic bearing 10.
And a front angular contact ball bearing 5 provided on the front side of the front radial magnetic bearing 20.

[0004] Between the rear radial magnetic bearing 10 and the rear angular ball bearing 2, four sensors 16 for detecting the position of the main shaft 1 in the radial direction are provided in the same plane in the radial direction, and the front radial is provided. Between the magnetic bearing 20 and the front angular contact ball bearing 5, four sensors 25 are provided on the same plane in the same radial direction and detect the radial position of the main shaft 1, and detect the axial position of the main shaft 1. One sensor 39 is provided.

In FIG. 1, reference numeral 4 denotes a drive rotor, which constitutes a part of a built-in drive motor for rotating the main shaft 1 about an axis. It should be noted that a housing for supporting each component of the stator of the drive motor and the spindle head is not shown.

The rear radial magnetic bearing 10 includes a rotor 14 formed by laminating ring-shaped metal plates, a holding member 15 for holding the rotor 14, a laminated body 12 formed by laminating metal plates, and The holding member 15 has an inner diameter portion fitted and fixed to the main shaft 1, and the holding member 15 is fixed to the stator 11. It is held in a housing (not shown). Further, the four stators 11 are evenly arranged along the outer peripheral surface of the rotor 14, and the four sensors 16 are also disposed along the outer peripheral surface of the main shaft 1, and They are evenly arranged with a corresponding relationship. The stator 11
A gap (air gap) of, for example, about 0.5 mm is provided between the rotor and the rotor 14.

The front radial magnetic bearing 20 includes a rotor 24 formed by laminating ring-shaped metal plates, a laminate 22 formed by laminating metal plates, and a laminate 22 formed by laminating metal plates.
The rotor 24 has an inner diameter portion fitted and fixed to the main shaft 1 and the stator 21 is fixed to the housing (not shown). ) Is held. Further, the four stators 21 are evenly arranged along the outer peripheral surface of the rotor 24, and the four sensors 25 are similarly disposed along the outer peripheral surface of the main shaft 1, and They are evenly arranged with a corresponding relationship. As in the rear radial magnetic bearing 10, a gap (air gap) of, for example, about 0.5 mm is provided between the stator 21 and the rotor 24. The main shaft 1 is formed with two flange portions 6 and 7. The outer peripheral surface of the flange portion 7 is detected by the sensor 25, and the lower end surface thereof is detected by the sensor 39. . The front side of the rotor 24 is locked by the flange 6.

The thrust magnetic bearing 30 has a rear stator 32 having a rotor 31 whose inner diameter is externally fitted to and fixed to the main shaft 1, a coil 33 formed in a ring shape, and a holding ring 34 holding the coil 33. And a front stator 35 comprising a coil 36 also formed in a ring shape and a holding ring 37 for holding the coil 36, and a spacer 38 provided between the rear stator 32 and the front stator 35. A flange 31a is formed on the outer periphery of the rotor 31.
1a is located between the rear stator 32 and the front stator 35. Also, a gap (air gap) of, for example, about 0.5 mm is provided between the flange portion 31a and the rear stator 32 and between the flange portion 31a and the front stator 35.

The control means 41 includes the coils 13, 2
A predetermined power is supplied to the coils 3, 33, and 36. Upon receiving detection signals from the sensors 16, 25, and 39, currents flowing through the coils 13, 23, 33, and 36 are adjusted. I have.

When predetermined electric power is supplied to the coils 13, 23, 33 and 36 by the control means 41, the stator 11 of the rear radial magnetic bearing 10, the stator 21 of the front radial magnetic bearing 20, and the Rear stator 32 and front stator 35 of thrust magnetic bearing 30
Each become an electromagnet, whereby the rotor 1
4, 24 and 31 are respectively sucked.

In the rear radial magnetic bearing 10, the four stators 11 apply suction force in four directions to the rotor 14, and similarly in the front radial magnetic bearing 20, four stators 21 generate four directions. An attractive force acts on the rotor 24, and thus the rear radial magnetic bearing 10 and the front radial magnetic bearing 20 cause the main shaft 1 to rotate.
Are supported in the radial direction.

As described above, the radial position of the main shaft 1 is detected by the sensors 16 and 25, and the main shaft 1 is deviated from the neutral position between the stators 11 and the neutral position between the stators 21. If the position is shifted from the position, the position shift is detected by the sensors 16 and 25.
Respectively, and based on this detection signal,
The electric power supplied to each of the stators 11 and 21 is adjusted by the control means 41. That is, in the interval between each stator 11 and the rotor 14, and in the interval between each stator 21 and the rotor 24, the supply power is increased for the stator 11 and the stator 21 in which the interval is wider than the reference interval, While the suction force is increased, the power supplied to the stators 11 and 21 whose intervals are narrower than the reference interval is reduced, and the suction force is reduced. Thereby, the main shaft 1 is always located between the stators 11 and the stator 21.
It is controlled to be located at a neutral position between the two.

Further, in the thrust magnetic bearing 30, the rear stator 32 and the front stator 35 cause the flange 31a of the rotor 31 to receive both front and rear (up and down) attracting forces.
It is supported in the axial direction so as to be located at an intermediate position between the front stator 2 and the front stator 35.

As described above, the axial position of the main shaft 1 is detected by the sensor 39, and if the main shaft 1 is displaced from the intermediate position between the rear stator 32 and the front stator 35, the positional deviation is detected. The rear stator 3 is detected by a sensor 39 and based on the detection signal.
2 and the electric power supplied to the front stator 35 are adjusted by the control means 41. That is, in the interval between the rear stator 32 and the flange portion 31a of the rotor 31, and in the interval between the front stator 35 and the flange portion 31a, the rear stator 3 is wider than the reference interval.
The power supplied to the second or front stator 35 is increased to increase the attraction force, while the power is supplied to the rear stator 32 or the front stator 35 whose interval is narrower than the reference interval. The power is reduced and the suction force is reduced. Thus, the rotor 3
1 is always controlled to be located at an intermediate position between the rear stator 32 and the front stator 35, whereby the main shaft 1 is properly supported in the axial direction.

According to this spindle head, the spindle 1
Since the main shaft 1 is supported in the radial and axial directions by the attractive force of the electromagnet without directly contacting the main shaft 1, the main shaft 1 rotating at an extremely high rotation speed can be properly supported. ing.

Incidentally, the angular ball bearings 2 and 5 are provided so as to have a gap (air gap) of, for example, about 0.2 mm between the inner ring portion and the main shaft 1. It does not function as the main shaft 1 when an unexpected abnormality such as a power outage or failure occurs.
Are supported in the radial direction and the axial direction, and the stators 11 and 21, the rear stator 32 and the front stator 3 are supported.
5 and a role to prevent each part of the rotors 14, 24, 31 from being damaged. For this reason, the air gap in the angular ball bearings 2 and 5 is smaller than the air gap in the rear radial magnetic bearing 10, the front radial magnetic bearing 20, and the thrust magnetic bearing 30.

[0017]

However, in the spindle head in which the main shaft 1 is supported by the magnetic bearings 10, 20, 30 described above, the high-speed rotation of the main shaft 1 is required due to the characteristics of the magnetic bearings 10, 20, 30. Although the dynamic rigidity at the time (rigidity against vibration) is high, there is a problem that the dynamic rigidity at the time of low-speed rotation is lower than that of the rolling bearing. That is, at the time of low-speed rotation, the main shaft 1 tends to resonate with external vibration such as vibration accompanying processing, and therefore, high-precision processing cannot be performed.

FIG. 3 shows an example of data relating to the dynamic rigidity of the spindle head. As shown in the figure, in this spindle head, when the frequency f is 125 (Hz) (converted to the number of revolutions of the spindle 1 is 7500 rpm), the dynamic rigidity K shows a minimum of 50 (gf / μm). Was. It is said that a dynamic stiffness of 1000 (gf / μm) or more is required in ordinary cutting. When this spindle head is viewed, the frequency f is 250 (Hz) (15,000 rpm when converted into the rotation speed of the spindle 1). It is considered that the dynamic rigidity is insufficient in the following rotation range. The broken line in the figure is
The figure shows the dynamic rigidity of a spindle head in which the spindle 1 is supported only by rolling bearings.
When the spindle 1 is supported by the rolling bearing, the spindle head has a desired dynamic rigidity in a rotation range of 15000 rpm or less.

Among various types of machining, there is a machining that requires the spindle 1 to be rotated at an extremely high speed, such as in the case of drilling an ultra-small diameter hole, while the spindle 1 is rotated at a low speed, such as tapping. There are processes that need to be performed, and these processes
In order to perform the operation with high accuracy using a single machine tool, it is necessary that the spindle head has a certain or more dynamic rigidity in all regions from a low speed region to an ultra high speed region.

The present invention has been made in view of the above circumstances, and a method of supporting a main shaft capable of providing a fixed dynamic rigidity even in a low-speed region when the main shaft is supported by a magnetic bearing. An object of the present invention is to provide a spindle head having dynamic rigidity.

[0021]

According to a first aspect of the present invention, there is provided a method for rotatably supporting a main shaft of a machine tool, the method comprising: When the rotation speed is higher than a certain rotation speed, the main shaft is supported by the thrust magnetic bearing and the radial magnetic bearing. On the other hand, when the rotation speed of the main shaft is lower than the certain rotation speed, the thrust magnetic bearing and the radial magnetic bearing are used. The main shaft is supported by a bearing and an angular ball bearing, and the means for supporting the main shaft is changed according to the rotation speed of the main shaft.

This method is preferably implemented by the spindle head according to the second aspect of the present invention. That is, the invention according to claim 2 provides a main shaft, a thrust magnetic bearing and a radial magnetic bearing rotatably supporting the main shaft, a housing supporting the thrust magnetic bearing and the radial magnetic bearing, the thrust magnetic bearing, In a spindle head of a machine tool comprising control means for controlling the operation of the radial magnetic bearing, a taper portion having a smaller diameter toward a front side of the spindle is provided in a part of the spindle, and An angular ball bearing is disposed at a position corresponding to the tapered portion, and an inner diameter portion of an inner ring of the angular ball bearing is formed in a tapered shape having a smaller diameter toward a front side of the main shaft. When the rotation speed of the main shaft becomes lower than a certain rotation speed, the thrust magnetic force is applied to the thrust magnetic bearing so that the main shaft is attracted to the front side. When the rotation speed of the main shaft is lower than a certain rotation speed, the main shaft moves to the front side in the axial direction by the attraction force of the thrust magnetic bearing, and the taper portion of the main shaft is formed. The tapered portion of the inner ring of the angular contact ball bearing is engaged so that the main shaft is supported by the angular contact bearing.

As described above, according to the present invention, when the rotational speed of the main shaft is higher than a certain rotational speed, the main shaft is supported by the thrust magnetic bearing and the radial magnetic bearing, while the main shaft rotates. When the number of rotations becomes lower than a certain number of rotations, the main shaft moves to the front side in the axial direction by the attraction force of the thrust magnetic bearing, and the tapered portion of the main shaft and the tapered portion of the angular contact ball bearing inner ring engage. Thereby, the main shaft is supported by the angular ball bearing, and is supported by the thrust magnetic bearing and the radial magnetic bearing. Thus, according to the present invention, the means for supporting the main shaft is changed according to the rotation speed of the main shaft.

By the way, as described above, in the spindle head in which the spindle is supported by the magnetic bearing, the dynamic rigidity in the low-speed rotation region below a specific rotation speed is lower than the rigidity required for actual cutting. In a spindle head having a spindle supported by a rolling bearing, the dynamic rigidity in the rotation region is higher than the rigidity required for actual cutting.

According to the present invention, in consideration of the above-mentioned characteristics relating to the dynamic rigidity of the spindle head supporting the spindle by the magnetic bearing, the rotational speed of the spindle at which the dynamic rigidity is lower than the rigidity required for actual cutting is determined. In the rotation region higher than the rotation speed, the main shaft is supported by the thrust magnetic bearing and the radial magnetic bearing, and in the rotation region lower than the rotation speed, the angular ball bearing, the thrust magnetic bearing, and the radial magnetic bearing are supported. Since the spindle can be supported by the bearing, the dynamic rigidity of the spindle head can be made higher than the rigidity required for actual cutting in the entire rotation range of the spindle. Will be able to do it.

As can be seen from the above description, the above-mentioned constant rotational speed is defined as a value obtained by referring to the rotational speed of the spindle at which the dynamic rigidity of the spindle head is lower than the rigidity required for actual cutting.
It refers to the number of rotations set arbitrarily.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a front view showing a schematic configuration of the spindle head according to the present embodiment.
Incidentally, as shown in FIG.
This is an improvement of the conventional spindle head shown in FIG. 4 described above, and most of the configuration is the same as the configuration of the conventional spindle head. Therefore, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 1, the spindle head according to the present embodiment has a point that a tapered portion 1a is formed in a part of the spindle 1, and an angular ball bearing 3 is provided at a position corresponding to the tapered portion 1a. The above-described conventional spindle head differs from the above-described conventional spindle head in that the configuration is different from that of the conventional spindle head.

The tapered portion 1a is provided on the main shaft 1 on the front side (lower side) of the flange portion 7, and is provided so as to have a smaller diameter toward the front side of the main shaft 1. I have.

The angular ball bearing 3 is disposed at a position corresponding to the tapered portion 1a of the main shaft 1. The inner diameter of the inner ring 3a is located at the front side of the main shaft 1 as shown in FIG. It is formed in a tapered shape having a smaller diameter as it goes.

The control means 40 has the following function in addition to the function of the control means 41 in the conventional spindle head described above. That is, when the rotation speed of the main shaft 1 becomes lower than a certain rotation speed, the control unit 40 makes the power supplied to the front stator 35 excessively larger than the power supplied to the rear stator 32, The suction force of the front stator 35 is made larger than the suction force of the rear stator 32, thereby moving the main shaft 1 to the front (downward) side. On the other hand, when the rotation speed of the main shaft 1 is higher than a certain rotation speed, the control unit 40 performs the same control as the above-described conventional control unit 41.

In the present embodiment, the number of rotations when the spindle 1 is moved to the front side is determined assuming that the spindle head has the dynamic rigidity shown in FIG. , The number of revolutions of the main shaft 1, ie, 15000r
20,000 rpm was set on the basis of pm with some margin. However, the number of revolutions is determined according to the characteristic relating to the dynamic rigidity of the spindle head, and is based on the number of revolutions of the spindle at which the dynamic rigidity of the spindle head is lower than the rigidity required for actual cutting. Is set arbitrarily.

The rotation speed of the spindle 1 is 20,000 rpm.
If it is higher than that, as shown in FIG. 2, a predetermined gap is provided between the tapered portion 1a of the main shaft 1 and the inner ring 3a of the angular ball bearing 3. On the other hand, when the rotation speed of the main shaft 1 becomes lower than 20000 rpm and the main shaft 1 moves to the front side, the tapered portion 1a of the main shaft 1 and the inner ring 3a of the angular ball bearing 3 engage, and the angular ball bearing 3 A predetermined preload is applied. In addition, even when the tapered portion 1a of the main shaft 1 and the inner ring 3a of the angular ball bearing 3 are engaged, a predetermined gap is secured between the front stator 35 and the flange portion 31a of the rotor 31. Has become.

Thus, according to this spindle head, when the rotation speed of the spindle 1 is higher than 20000 rpm, the spindle 1 is supported by the rear radial magnetic bearing 10, the front radial magnetic bearing 20, and the thrust magnetic bearing 30. On the other hand, when the rotation speed of the main shaft 1 becomes lower than 20000 rpm, the main shaft 1 moves to the front side in the axial direction due to the increased suction force of the front stator 35, and the tapered portion 1a of the main shaft 1 and the angular ball bearing 3 As a result of engagement of the inner ring 3a, the main shaft 1 has a rear radial magnetic bearing 10, a front radial magnetic bearing 20,
It is supported by the thrust magnetic bearing 30 and the angular ball bearing 3.

As described above, according to the spindle head, at the time of high-speed rotation, the rear radial magnetic bearing 10 and the front radial magnetic bearing 20 which provide dynamic rigidity higher than the rigidity required for actual cutting in the high-speed rotation region. In addition, the main shaft 1 is supported by the thrust magnetic bearing 30, and at the time of low-speed rotation, the main shaft 1 is supported by adding an angular ball bearing 3 that provides higher dynamic rigidity than rigidity required for actual cutting in the low-speed rotation region. As a result, the dynamic rigidity of the spindle head can be made higher than the rigidity required for actual cutting in the entire rotation range of the spindle 1 from low-speed rotation to high-speed rotation. Can be done.

The angular contact ball bearing 3 supports the main shaft 1 in the radial and axial directions when an unexpected abnormality such as a power failure or a failure occurs, so that the stators 11, 21 and the rear stator 32, It also plays a role in preventing each part of the front stator 35 and the rotors 14, 24, 31 from being damaged.

In this embodiment, the angular ball bearing 3 is provided on the front side of the spindle 1 in consideration of the static rigidity (bending rigidity and torsional rigidity) of the spindle head.

Although the embodiments of the present invention have been described above, it is needless to say that the specific aspects of the present invention are not limited to these. For example, the rear radial magnetic bearing 10, the front radial magnetic bearing 20, the thrust magnetic Bearing 3
The positional relationship where the 0 and angular ball bearings 3 are provided is not limited to this example. In addition, the method of supporting a spindle according to the present invention is not only applicable to the spindle head used in the vertical machine tool of the above example, but can be naturally applied to a spindle head used in a horizontal machine tool. The spindle head according to the present invention can of course be used for a horizontal machine tool.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic configuration of a spindle head according to an embodiment of the present invention.

FIG. 2 is an enlarged view showing a part of FIG. 1 in an enlarged manner.

FIG. 3 is a graph showing characteristics relating to dynamic rigidity of a conventional spindle head.

FIG. 4 is a front view showing a schematic configuration of a conventional spindle head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 2 Rear angular ball bearing 3 Angular ball bearing 4 Drive rotor 5 Front angular ball bearing 10 Rear radial magnetic bearing 11, 21, Stator 14, 24, 31 Rotor 20 Front radial magnetic bearing 30 Thrust magnetic bearing 31a Flange 32 Rear Stator 35 Front stator 16, 25, 39 Sensor 40, 41 Control means

Claims (2)

[Claims] 1. A method for rotatably supporting a spindle in a machine tool, wherein when the rotation speed of the spindle is higher than a certain rotation speed,
While the main shaft is supported by a thrust magnetic bearing and a radial magnetic bearing, when the rotation speed of the main shaft is lower than a certain rotation speed,
A main shaft in the machine tool, wherein the main shaft is supported by a thrust magnetic bearing, a radial magnetic bearing, and an angular ball bearing, and the means for supporting the main shaft is changed according to the rotation speed of the main shaft. Support method. 2. A main shaft, a thrust magnetic bearing and a radial magnetic bearing rotatably supporting the main shaft, a housing supporting the thrust magnetic bearing and the radial magnetic bearing,
In a spindle head of a machine tool comprising control means for controlling operations of the thrust magnetic bearing and the radial magnetic bearing, a part of the spindle has a tapered portion having a smaller diameter toward a front side of the spindle. An angular contact ball bearing is provided at a position corresponding to the tapered portion of the main shaft, and the inner diameter of the inner ring of the angular contact ball bearing is formed in a tapered shape having a smaller diameter toward the front side of the main shaft. And the control means controls the thrust magnetic bearing so that when the rotation speed of the main shaft becomes lower than a certain rotation speed, the main shaft is drawn to the front side by the attraction force of the thrust magnetic bearing. When the rotation speed of the main shaft is lower than a certain rotation speed, the main shaft moves to the front side in the axial direction by the attraction force of the thrust magnetic bearing, and the taper of the main shaft is formed. A spindle head of a machine tool, wherein a portion and a tapered portion of an inner ring of the angular ball bearing are engaged with each other so that the spindle is supported by the angular ball bearing.