JP2000167739A - Machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide constant dynamic rigidity even in a low speed region when a main spindle is supported by a magnetic bearing. SOLUTION: In a machine tool 1 provided with a main spindle head 2' supporting a main spindle 3' by a thrust magnetic bearing 30 and radial magnetic bearings 10, 20 so as to rotate freely, a tapered part is provided on the front side of the main spindle 3', an angular ball bearing 4 is arranged at a position corresponding to the tapered part of the main spindle 3', an inside diameter part of its inner ring is formed into a tapered shape, and the main spindle 3' is pulled to the front side due to attraction force of the thrust magnetic bearing 30 when the number of revolutions of the main spindle 3' is reduced below a fixed number of revolutions. A tool compensation data change means 46 changing tool compensation data used in the drive and control in accordance with the number of revolutions of the main spindle 3' is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool having a main shaft supported by magnetic bearings.

[0002]

2. Description of the Related Art FIG. 4 shows a vertical machining center as an example of the machine tool in which a main shaft is supported by magnetic bearings. FIG. 4 is a front view partially showing a main part of a conventional vertical machining center in a block diagram.

As shown in FIG. 4, a (vertical) machining center 100 includes a spindle head 2 for rotatably supporting a spindle 3, a table (not shown) for fixing and supporting a workpiece, and a table (not shown). (Not shown) and a support base (bed, column, etc.) for supporting the spindle head 2 (not shown);
Driving for moving a table (not shown) and / or the spindle head 2 and relatively moving the table (not shown) and the spindle head 2 in three-dimensional three-axis directions (X axis, Y axis, Z axis). And a numerical controller 40 for numerically controlling the operation of the driving means (not shown). Hereinafter, details of each unit will be described.

(Spindle Head) The spindle head 2 includes a spindle 3 whose axis is oriented vertically, a rear radial magnetic bearing 10 for supporting a rear side (upper side) of the spindle 3 in a radial direction, and a spindle. 3, a front radial magnetic bearing 20, which also supports the front side (lower side) in the radial direction, the rear radial magnetic bearing 10, and the front radial magnetic bearing 20.
A thrust magnetic bearing 30 for supporting the main shaft 3 in the axial direction therebetween, a rear angular ball bearing 5 provided on the rear side of the rear radial magnetic bearing 10, and a front magnetic ball bearing 20 provided on the front side of the front radial magnetic bearing 20. And a front angular ball bearing 7. The operation of the rear radial magnetic bearing 10, the front radial magnetic bearing 20, and the thrust magnetic bearing 30 is controlled by the numerical controller 40.

Also, between the rear radial magnetic bearing 10 and the rear angular ball bearing 5, four sensors 16 for detecting the position of the main shaft 3 in the radial direction are provided on the same plane in the radial direction. Between the magnetic bearing 20 and the front angular contact ball bearing 7, four sensors 25 are provided on the same plane in the radial direction and detect the radial position of the main shaft 3, and detect the axial position of the main shaft 3. Two sensors 39 are provided.

In FIG. 1, reference numeral 6 denotes a drive rotor, which constitutes a part of a drive motor of a built-in system for rotating the main shaft 3 about an axis. The stator of the drive motor and the components of the spindle head 2 are supported by a housing (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 3, 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 3, and They are evenly arranged with a corresponding relationship. A gap (air gap) of, for example, about 0.5 mm is provided between the stator 11 and the rotor 14.

The front radial magnetic bearing 20 includes a rotor 24 formed by laminating ring-shaped metal plates, a laminate 22 also 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 3 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 also disposed along the outer peripheral surface of the main shaft 3, with the stator 21. They are evenly arranged with a corresponding relationship. As in the rear radial magnetic bearing 10, the stator 21
A gap (air gap) of, for example, about 0.5 mm is also provided between the rotor and the rotor 24. In addition, the spindle 3
Are formed with two flange portions 8 and 9. The outer peripheral surface of the flange portion 9 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 8.

The thrust magnetic bearing 30 has a rear stator 32 comprising a rotor 31 whose inner diameter is externally fitted to and fixed to the main shaft 3, 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 above-mentioned angular ball bearings 5, 7 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 3. It does not function as the main shaft 3 when an unexpected abnormality such as a power failure 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 5 and 7 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.

(Numerical control unit) The numerical control unit 40
Is connected to a rotary encoder or the like provided in the driving means (not shown), and calculates a position of the spindle 3 (spindle head 2) in a machine coordinate system as needed, and is used for machining. The tool correction data storage unit 43 storing tool correction data (FIG. 5) related to the tool length of the tool to be performed, the tool correction data stored in the tool correction data storage unit 43, and the position coordinate calculation unit 42 The driving means (not shown) based on the position data
A drive control unit 41 for numerically controlling the operation of the motor, a bearing control unit 44 for supplying power to the rear radial magnetic bearing 10, the front radial magnetic bearing 20, and the thrust magnetic bearing 30 to control the operation, and the sensor 16 , 25, and 39, and receives signals from them, and detects a displacement of the main shaft 3.

As described above, the bearing control unit 44
A predetermined power is supplied to the coils 13, 23, 33, 36, and the coils 13, 23, 33, 3 are supplied in accordance with the displacement of the main shaft 3 detected by the displacement detector 45.
Adjust the current supplied to 6.

When a predetermined power is supplied from the bearing control unit 44 to the coils 13, 23, 33, and 36, 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 the front stator 35 of the 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 forces in four directions to the rotor 14, and similarly in the front radial magnetic bearing 20, the four stators 21 generate four directions. Attraction force acts on the rotor 24, and the main shaft 3 is radially supported by the rear radial magnetic bearing 10 and the front radial magnetic bearing 20.

As described above, the sensors 16 and 2
5, the radial position of the main shaft 3 is detected. When the main shaft 3 deviates from the neutral position between the stators 11 and when the main shaft 3 deviates from the neutral position between the stators 21, this positional deviation Sensor 16 and sensor 25
Respectively, and based on this detection signal,
The power supplied to each of the stators 11 and 21 is adjusted by the bearing control unit 44. 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 3 is always kept 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 portion 31a of the rotor 31 to receive suction force in both front and rear (up and down) directions.
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 main shaft 3 is detected by the sensor 39.
Is detected in the axial direction, and when the main shaft 3 is displaced from the intermediate position between the rear stator 32 and the front stator 35, the displacement is detected by the sensor 39, and based on this detection signal, The rear stator 32
The power supplied to the front stator 35 is adjusted by the bearing control unit 44. 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 32 is wider than the reference interval.
Alternatively, the power supplied to the front stator 35 is increased, and the suction force is increased. On the other hand, the power supplied to the rear stator 32 or the front stator 35 whose interval is narrower than the reference interval is increased. Is reduced,
The suction force is reduced. In this way, the rotor 31 is controlled so as to be always located at an intermediate position between the rear stator 32 and the front stator 35, whereby the main shaft 3 is properly supported in the axial direction.

According to the machine tool 100, the main shaft 3 is supported in the radial direction and the axial direction by the attractive force of the electromagnet without directly contacting the main shaft 3, so that the rotating speed is extremely high. The main shaft 3 can be appropriately supported.

[0019]

However, in the spindle head 2 in which the spindle 3 is supported by the magnetic bearings 10, 20, 30 described above, due to the characteristics of the magnetic bearings 10, 20, 30, the speed of the spindle 3 is high. Although the dynamic rigidity (rigidity against vibration) during rotation is sufficient, there is a problem that the dynamic rigidity during low-speed rotation is low. That is, at the time of low-speed rotation, the main shaft 3 tends to resonate with external vibration such as vibration accompanying processing, and therefore, high-precision processing cannot be performed.

FIG. 6 shows an example of data relating to the dynamic rigidity of the spindle head 2. As shown in the drawing, in the spindle head 2, when the frequency f is 125 Hz (when converted into the number of revolutions of the spindle 3 is 7,500 rpm), the dynamic rigidity K shows a minimum value of 50 gf / μm. It is said that a dynamic stiffness of 1000 gf / μm or more is required in ordinary cutting. When the spindle head 2 is viewed, the frequency f is 250 Hz (which is 15
It is considered that the dynamic stiffness is insufficient in the rotation range of 000 rpm or less. The broken line in the figure shows the dynamic rigidity of the spindle head 2 in which the spindle 3 is supported only by the rolling bearing. As shown in the figure, when the spindle 3 is supported by the rolling bearing, The head 2 has a desired dynamic rigidity in a rotation range of 15,000 rpm or less.

Among various types of machining, there is machining that requires the spindle 3 to be rotated at an ultra-high speed, as in the case of drilling an ultra-small diameter hole, while rotating the spindle 3 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 it is an object of the present invention to provide a machine tool capable of having a constant dynamic rigidity even in a low speed region when a main shaft is supported by a magnetic bearing. I do.

[0023]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a main shaft, a thrust magnetic bearing and a radial magnetic bearing rotatably supporting the main shaft, and the thrust magnetic bearing and the radial magnetic bearing. A spindle head having a housing for supporting the workpiece, support means for fixing and supporting the workpiece, drive means for moving the support means and / or the spindle head, and position detection means for detecting the position of the spindle. Bearing control means for controlling the operation of the thrust magnetic bearing and the radial magnetic bearing; and numerical control means for numerically controlling the operation of the drive means based on the stored tool correction data and the position data detected by the position detection means. And a taper portion having a smaller diameter toward the front side of the main shaft is provided on a part of the main shaft, and a taper of the main shaft is provided. The angular contact ball bearing is disposed at a position corresponding to the portion, and the inner diameter portion 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. When the rotation speed of the main shaft is lower than a predetermined rotation speed, the thrust magnetic bearing is controlled so as to draw the main shaft toward the front side by the attraction force of the thrust magnetic bearing, and the main spindle head is configured. Tool correction data changing means for changing the tool correction data used for the drive control according to the rotation speed of the spindle, and when the rotation speed of the spindle becomes lower than a predetermined rotation speed, the spindle becomes the thrust magnetic. Due to the attraction force of the bearing, the main shaft moves to the front side in the axial direction, and the tapered portion of the main shaft engages with the tapered portion of the inner ring of the angular contact ball bearing. The tool correction data supported and used by the bearing is changed by the tool correction data changing means in accordance with the rotational speed of the spindle, and the driving means is numerically controlled based on the changed tool correction data. It is characterized by having comprised in.

According to the present invention, when the rotational speed of the main shaft is higher than a predetermined rotational speed, the main shaft is supported by the thrust magnetic bearing and the radial magnetic bearing, while the rotational speed of the main shaft is constant. When the number is lower than the number, the attraction force of the thrust magnetic bearing moves the main shaft toward the front in the axial direction, and the tapered portion of the main shaft engages with the tapered portion of the inner ring of the angular ball bearing. Are supported by the angular ball bearings and 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, the rotational speed of the spindle at which the dynamic rigidity is lower than the rigidity required for actual cutting is determined in consideration of the dynamic rigidity of the spindle head supporting the spindle by the magnetic bearing. 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 understood from the above description, the above-mentioned constant rotational speed is defined as a value based on 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.

According to the present invention, when the rotation speed of the spindle becomes lower than a predetermined rotation speed and the spindle moves to the front side in the axial direction, the tool correction data to be used is changed by the tool correction data changing means. The drive of the spindle head is controlled based on the changed tool correction data.

The rotation speed of the main shaft is higher than a certain rotation speed,
When the main shaft is controlled to be located at the rear side in the axial direction, and when the rotation speed of the main shaft is lower than a certain rotation speed and the main shaft is controlled to be positioned at the front side in the axial direction. Since the position of the cutting edge in the axial direction of the tool mounted on the spindle is different in both cases, in both cases, if the drive of the spindle head is controlled using the same tool correction data to perform the machining, the depth of the hole to be machined is In addition, there is a problem that the thread depth and the boring processing depth are not finished to predetermined dimensions, that is, the processing accuracy is deteriorated.

According to the present invention, the drive of the spindle head is controlled by using the tool correction data corresponding to the position in the axial direction of the spindle whose position in the axial direction is controlled by the rotation speed. Such a problem does not occur, and it is possible to prevent the processing accuracy from deteriorating due to the spindle position control described above.

[0031]

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 partially showing a main part of a vertical machining center according to the present embodiment in a block diagram. As shown in the figure, the (vertical) machining center 1 according to the present embodiment is an improvement of the above-described conventional machining center 100 shown in FIG.
The configuration is the same as that of 00. Therefore, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIGS. 1 and 2, a spindle head 2 'according to the present embodiment has a tapered portion 3
a, and that an angular ball bearing 4 is provided at a position corresponding to the tapered portion 3a.
The configuration of the numerical control device 40 'is different from that of the bearing control unit 44 in that the function of the bearing control unit 44' is different from that of the bearing control unit 44, and the contents of the tool correction data stored in the tool correction data storage unit 43 'are different. The configuration of the conventional numerical control device 40 is different from that of the above-described conventional numerical control device 40 in that the configuration is different from that of the tool correction data storage unit 43 and that a tool correction data change unit 46 is provided.
Hereinafter, details of each unit will be described.

(Spindle Head) As described above, the spindle 3 ′ of the spindle head 2 ′ of the present embodiment is located on the front side (lower side) of the flange 9, toward the front side of the spindle 3 ′. Is formed, the tapered portion 3a having a smaller diameter is formed.
The angular ball bearing 4 is provided at a position corresponding to. As shown in FIG. 2, the angular contact ball bearing 4 is formed in a tapered shape in which the inner diameter of the inner race 4a becomes smaller in diameter toward the front side of the main shaft 3 '.

(Numerical control unit) The bearing control unit 44 '
Has the following functions in addition to the functions of the conventional bearing control unit 44 described above. That is, the bearing control unit 44 '
When the rotation speed of the main shaft 3 ′ is lower than a certain rotation speed, the power supplied to the front stator 35 is made larger than the power supplied to the rear stator 32, and the suction by the front stator 35 is performed. The main shaft 3 'is moved toward the front (downward) so that the force is greater than the suction force by the rear stator 32. On the other hand, when the rotation speed of the main shaft 3 'is higher than a certain rotation speed, the bearing control means 4
4 'performs the same control as the above-described conventional bearing control unit 44.

In the present embodiment, the number of rotations when the spindle 3 'is moved to the front side is required for actual cutting assuming that the spindle head 2' has the dynamic rigidity shown in FIG. The number of revolutions of the main shaft 3 ′, which falls below the dynamic rigidity, ie, 150
20000rpm with a little margin based on 00rpm
m. However, the number of revolutions is determined according to the characteristics of the dynamic rigidity provided in the spindle head 2 ′, and the rotational speed of the spindle in which the dynamic rigidity of the spindle head 2 ′ is lower than the rigidity required for actual cutting. It is arbitrarily set based on the number of rotations.

The rotation speed of the main shaft 3 'is 20,000 rpm.
If it is higher than that, as shown in FIG. 2, a predetermined gap is formed between the tapered portion 3a of the main shaft 3 'and the inner ring 4a of the angular ball bearing 4, and the rotational speed of the main shaft 3' Is lower than 20,000 rpm, and the main shaft 3 ′ moves forward, the tapered portion 3 a of the main shaft 3 ′ engages with the inner ring 4 a of the angular ball bearing 4, and a predetermined preload acts on the angular ball bearing 4. It is supposed to. Also, when the tapered portion 3a of the main shaft 3 'is engaged with the inner ring 4a of the angular ball bearing 4, a predetermined gap is ensured between the front stator 35 and the flange portion 31a of the rotor 31. It has become.

The tool correction data storage unit 43 'stores tool correction data used when the rotation speed of the spindle 3' is higher than 20000 rpm, that is, tool correction data at the time of high-speed rotation shown in FIG. Table and tool correction data used when the rotation speed of the spindle 3 ′ is lower than 20000 rpm and the spindle 3 ′ is moved to the front side, that is, the tool at the time of low-speed rotation shown in FIG. Both of the correction data tables are stored. The tool correction data at the time of low-speed rotation is calculated by adding the axial movement amount of the spindle 3 ′ to the tool correction data at the time of high-speed rotation. If the tool is moved by 0.3 mm, 0.3 mm is added to the tool correction amount of each tool shown in FIG.
The tool correction amount shown in (b) is obtained.

The tool correction data changing section 46 receives the control signal from the bearing control section 44 'and converts the tool correction data according to the rotation speed of the main shaft 3', that is, the axial position of the main shaft 3 '. The tool correction data is selected from the tool correction data stored in the tool correction data storage unit 43 'and transmitted to the drive control unit 41.
Specifically, when the spindle 3 'is in the high-speed rotation position, tool correction data for the corresponding tool is read from the tool correction data table at the time of high-speed rotation and transmitted to the drive control unit 41. , The tool correction data for the corresponding tool is read from the tool correction data table at the time of low-speed rotation and transmitted to the drive control unit 41. The drive control unit 41 numerically controls the drive unit (not shown) using the received tool correction data.

Thus, according to the machining center 1, when the rotation speed of the main shaft 3 ′ is higher than 20000 rpm, the main shaft 3 ′ is connected to 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 3 'becomes lower than 20000 rpm, the increased suction force of the front stator 35 moves the main shaft 3' to the front side in the axial direction, and the tapered portion 3a of the main shaft 3 ' As a result, the main shaft 3 ′ is supported by the rear radial magnetic bearing 10, the front radial magnetic bearing 20, the thrust magnetic bearing 30, and the angular ball bearing 4.

As described above, at the time of high-speed rotation, the main shaft is formed by the rear radial magnetic bearing 10, the front radial magnetic bearing 20, and the thrust magnetic bearing 30, which provide dynamic stiffness higher than required for actual cutting in the high-speed rotation region. 3 '
During low-speed rotation, the main shaft 3 ′ is supported by adding an angular ball bearing 4 that provides a higher dynamic rigidity than the rigidity required for actual cutting in the low-speed rotation region. The dynamic rigidity of the head 2 'can be made higher than the rigidity required for actual cutting in the entire rotation range of the main shaft 3' from low-speed rotation to high-speed rotation, so that any machining can be performed with high precision. Will be able to do it.

The angular contact ball bearing 4 supports the main shaft 3 'in the radial and axial directions when an unexpected abnormality such as a power failure or failure occurs, for example, so that the stators 11 and 21 and the rear stator 32 are supported. , Front stator 35
And also serves to prevent the rotors 14, 24, 31 from being damaged. In this embodiment, the angular ball bearing 4 is provided on the front side of the spindle 3 'in consideration of the static rigidity (bending rigidity and torsional rigidity) of the spindle head 2'.

According to the machining center 1,
The tool correction data corresponding to the rotation speed of the main shaft 3 ′, that is, the axial position of the main shaft 3 ′ is processed by the tool correction data changing unit 46 from the tool correction data stored in the tool correction data storage unit 43 ′. The driving means (not shown) is driven by the drive control unit 41 based on the extracted tool correction data. Specifically, the rotation speed of the main shaft 3 ′ is 2
If the spindle 3 ′ is higher than 0000 rpm and the spindle 3 ′ is located on the rear side in the axial direction, the tool correction data changing unit 46
3 is stored in the tool correction data storage unit 43 ′,
The tool correction data for the corresponding tool is read from the tool correction data table at the time of high-speed rotation shown in (a) and transmitted to the drive control unit 41, and the rotation speed of the spindle 3 'is 2
0000 rpm or less, and when the main shaft 3 ′ is controlled to be located on the front side in the axial direction, FIG.
From the tool correction data table at the time of low-speed rotation shown in (b), tool correction data for the corresponding tool is read and transmitted to the drive control unit 41. The drive control unit 41 numerically controls the drive unit (not shown) using the received tool correction data.

When the rotational speed of the main shaft 3 'is higher than 20,000 rpm and the main shaft 3' is controlled so as to be located on the rear side in the axial direction, the rotational speed of the main shaft 3 'is 20,000.
rpm or less, and when the main shaft 3 ′ is controlled to be located on the front side in the axial direction, the cutting edge position in the axial direction of the tool mounted on the main shaft 3 ′ is different. If the spindle head 2 'is driven and controlled using the same tool correction data to perform machining, the machined hole depth, screw depth, and boring machining depth will not be finished to specified dimensions, that is, machining accuracy will be poor. The problem arises. In this example, the spindle head 2 'is numerically controlled using tool correction data corresponding to the axial position of the spindle 3' whose position in the axial direction is drive-controlled by the rotational speed. It is possible to prevent the machining accuracy from deteriorating due to the position control of the spindle 3 'without causing any serious problem.

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 this. 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.

In the above example, the tool correction data used when the main shaft 3 'is located at the rear side in the axial direction and the main shaft 3'
Are stored in the tool correction data storage unit 43 ', and these data are selectively used in accordance with the position of the spindle 3'. The present invention is not limited to this. For example, any one of the above-described tool correction data is stored in the tool correction data storage unit 43 ′, and the stored tool correction data is stored in the tool correction data changing unit 46 in the axial direction of the spindle 3 ′. The amount may be added or subtracted to calculate tool correction data corresponding to the position of the spindle 3 ', and the drive of the spindle head 2' may be controlled based on the calculated tool correction data.

In the above example, the tool correction data changing unit 4
6 receives the control signal of the bearing control unit 44 'and recognizes the axial position of the spindle 3', but the tool correction data changing unit 46 receives the control signal of the drive control unit 41 and You may comprise so that the position of 3 'of an axial direction may be recognized.

[Brief description of the drawings]

FIG. 1 is a front view partially showing a main part of a vertical machining center according to an embodiment of the present invention in a block diagram.

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

FIG. 3 is an explanatory diagram for describing tool correction data stored in a tool correction data storage unit of the vertical machining center according to the embodiment.

FIG. 4 is a front view partially showing a main part of a conventional vertical machining center in a block diagram.

FIG. 5 is an explanatory diagram for explaining tool correction data stored in a tool correction data storage unit of a conventional vertical machining center.

FIG. 6 is a graph showing characteristics relating to dynamic rigidity of a conventional spindle head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Machining center 2 Main shaft head 3 Main shaft 4 Front angular ball bearing 5 Rear angular ball bearing 6 Drive rotor 10 Rear radial magnetic bearing 11, 21 Stator 14, 24, 31 Rotor 20 Front radial magnetic bearing 30 Thrust magnetic bearing 31a Flange part 32 Rear stator 35 Front stator 16, 25, 39 Sensor 40 Numerical control unit 41 Drive control unit 42 Position calculation unit 43, 43 'Tool correction data storage unit 44, 44' Bearing control unit 45 Displacement detection unit 46 Tool correction data change unit

Claims (1)

[Claims] 1. A spindle head having 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, and a work to be fixed and supported. Supporting means, a driving means for moving the supporting means and / or the spindle head, and a position detecting means for detecting a position of the spindle.
Bearing control means for controlling the operation of the thrust magnetic bearing and the radial magnetic bearing; and numerical control means for numerically controlling the operation of the drive means based on the stored tool correction data and the position data detected by the position detection means. In a machine tool comprising: a part of the main shaft, a tapered portion having a smaller diameter toward the front side of the main shaft is provided, and an angular 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 ball bearing is formed in a tapered shape having a smaller diameter toward the front side of the main shaft. When lowered, the thrust magnetic bearing is configured to be controlled so as to draw the main shaft toward the front side by the attraction force of the thrust magnetic bearing, and the main shaft head is controlled. Providing tool correction data changing means for changing the tool correction data used for dynamic control in accordance with the rotation speed of the spindle; and when the rotation speed of the spindle is lower than a certain rotation speed, the spindle becomes the thrust magnetic bearing. Is moved toward the front side in the axial direction by the attraction force, and the tapered portion of the main shaft engages with the tapered portion of the inner ring of the angular ball bearing, whereby the main shaft is supported by the angular ball bearing and used. A machine tool wherein tool correction data is changed by the tool correction data changing means in accordance with the rotational speed of the spindle, and the driving means is numerically controlled based on the changed tool correction data. .