JPH1029101A - Magnetic bearing spindle device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the actual rigidity of a spindle while it is used by providing a rigidity measuring means for measuring spindle rigidity. SOLUTION: In upper and lower magnetic bearings 7 and 8, loads of X axis directions changed in sine wave shapes and kept always equal for size and direction in upper and lower directions are applied, and a spindle 5 is vibrated in the X axis direction. While the spindle 5 is vibrated, the X axis direction displacement of the spindle 5 in the positions of the upper and lower radial magnetic bearings 7 and 8 is measured based the outputs of X axis direction radial position sensors 10 and 11 and a sensor driving circuit 13. After this displacement measuring is finished, based on the result thereof, the X axis direction rigidity value of the spindle 5 in the tip of a tool 18 is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing spindle device, and more particularly to a magnetic bearing spindle device in which a spindle is supported in a non-contact manner by a plurality of sets of magnetic bearings, and more particularly, a magnetic bearing spindle device suitable for machine tools. About.

[0002]

2. Description of the Related Art As a magnetic bearing spindle device for a machine tool, there is known a device in which a spindle is contactlessly supported by a plurality of sets of magnetic bearings, for example, one set of axial magnetic bearings and two sets of radial magnetic bearings. . In this magnetic bearing spindle device, a tool is mounted on the tip of the spindle, and in general, the tool can be changed to a different type depending on the processing content. In addition, the magnetic bearing spindle device has a rotation speed range determined by the natural frequency of the spindle and the like, and when this is used for a machine tool, conventionally, in order to increase machining efficiency, the tool itself is required to be within the rotation speed range described above. In general, the spindle was rotated at the highest rotation speed allowed from the viewpoint of the strength.

In the magnetic bearing spindle device as described above, the rigidity of the spindle changes depending on the number of revolutions, and the relationship between the number of revolutions of the spindle and the rigidity (hereinafter referred to as "rigidity characteristics") depends on the presence or absence of a tool or a tool. Depends on the type. This is because the weight of the entire spindle (the combined weight of the spindle and the tool), the natural frequency, and the like change depending on whether the tool is mounted on the spindle or not, or depending on the type of the tool. .

As described above, the rigidity of the spindle varies depending on the number of rotations. Therefore, it is desirable to rotate the spindle at the rotational speed with the highest rigidity or at a rotational speed that provides a certain degree of rigidity. However, in the past, it was not possible to select the optimal rotation speed in consideration of the rigidity of the spindle when the tool was actually mounted, and to use the highest possible rotation speed from the viewpoint of the strength of the tool itself as described above. Because it is designed to rotate, it is not always possible to rotate at the optimum rotational speed in terms of rigidity, and the rigidity is not always sufficient at that rotational speed, and in some cases, processing due to insufficient rigidity In some cases, the ability was reduced.

A similar problem arises in magnetic bearing spindles other than those for machine tools when the rigidity of the spindle must be considered.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic bearing spindle device capable of measuring the actual rigidity of a spindle in a use state.

A second object of the present invention is to provide a magnetic bearing spindle device which requires a small number of components for measuring rigidity, in addition to the object of the first invention.

A third object of the present invention is to provide a magnetic bearing spindle device capable of measuring the rigidity of a part of a tool attached to the tip of a spindle in addition to the object of the second invention. And

A fourth object of the present invention is to provide a magnetic bearing spindle device capable of measuring the actual rigidity characteristics of a spindle in a use state and selecting an optimum rotational speed in terms of rigidity. .

A fifth object of the present invention is to provide a magnetic bearing spindle device in which, in addition to the object of the fourth invention, the addition of a configuration for measuring rigidity characteristics and selecting an optimum rotational speed is small. I do.

According to a sixth aspect of the present invention, in addition to the object of the fifth aspect, an optimum rotation speed is selected from the aspect of rigidity by measuring a rigidity characteristic of a portion of a tool mounted on a tip portion of a spindle. It is an object of the present invention to provide a magnetic bearing spindle device that can perform the above.

A seventh object of the present invention is to provide a magnetic bearing spindle device capable of selecting a rotational speed having the highest rigidity, in addition to the objects of the fourth, fifth or sixth invention.

According to an eighth aspect of the present invention, in addition to the object of the fourth, fifth or sixth aspect, a magnetic bearing spindle device capable of selecting the highest rotational speed among rotational speeds having a certain degree of rigidity or more. The purpose is to provide.

[0014]

According to a first aspect of the present invention, there is provided a magnetic bearing spindle device in which a spindle is supported in a non-contact manner by a plurality of sets of magnetic bearings, wherein rigidity measuring means for measuring the rigidity of the spindle is provided. It is characterized by having.

In this specification, the rigidity of the spindle refers to the displacement resistance (the difficulty of displacement) of the spindle to a radial load. Further, the rigidity of the spindle at an arbitrary position can be used as the rigidity of the spindle.

For example, each magnetic bearing includes a plurality of electromagnets for magnetically attracting the spindle. The magnetic bearing spindle device includes a position sensor for detecting the position of the spindle, an appropriate magnetic bearing control device, and the like. The magnetic bearing control device controls the exciting current supplied to the electromagnet of the magnetic bearing based on the output of the position sensor, whereby the spindle is held at a predetermined position.

As the magnetic bearing control device, a microcomputer or a digital signal processor (Digi
(digital signal processor) or the like. The digital signal processor refers to dedicated hardware that inputs a digital signal, outputs a digital signal, is software-programmable, and is capable of high-speed real-time processing. Hereinafter, this is abbreviated as “DSP”.

According to the first aspect of the present invention, since the rigidity measuring means for measuring the rigidity of the spindle is provided, the actual rigidity of the spindle in the use state can be measured, and the rigidity of the spindle in the use state is sufficient. Can be determined.

According to a second aspect of the present invention, in the first aspect of the present invention, the rigidity measuring means controls an exciting current supplied to the electromagnet of the magnetic bearing while the spindle is rotated at a predetermined rotation speed. Thus, the spindle is vibrated in a predetermined radial direction, a displacement of the spindle in the radial direction is measured, and a rigidity value of the spindle is calculated from the displacement.

In this case, the rigidity measuring means is provided in the magnetic bearing control device. As a magnetic bearing control device in that case, a digital type using a DSP is particularly suitable.

The radial displacement of the spindle can be measured by a radial position sensor inherent in the magnetic bearing spindle device. In addition, since the spindle can be excited by controlling the exciting current of the electromagnet originally provided in the magnetic bearing, means for controlling the exciting current of the electromagnet, the radial direction of the spindle based on the output of the radial position sensor, The means for measuring the displacement of the spindle and the means for calculating the rigidity of the spindle from the displacement need only be added as a program to the magnetic bearing control device, and there is no need to add a mechanical configuration for measuring the rigidity.

According to the second aspect of the present invention, there is no need to add a mechanical configuration for measuring the rigidity, and the number of configurations for measuring the rigidity can be reduced.

According to a third aspect of the present invention, in the first aspect of the present invention, a tool is mounted on a tip of the spindle, the magnetic bearing includes at least two sets of radial magnetic bearings, and the stiffness measuring means is provided on the spindle. While rotating at a predetermined number of revolutions, the spindle is vibrated in a predetermined radial direction by controlling an exciting current supplied to the electromagnet of the radial magnetic bearing, so that the spindle at the position of each radial magnetic bearing is controlled. The method is characterized in that a displacement of the spindle in a radial direction is measured, and a rigidity value of the spindle at the tip of the tool is calculated from the displacement.

According to the third aspect of the invention, similarly to the second aspect of the invention, there is no need to add a mechanical configuration for measuring the rigidity, and the number of configurations for measuring the rigidity can be reduced. . In addition, the actual rigidity of the spindle can be measured with the tool mounted on the tip of the spindle, and it can be determined whether the rigidity of the spindle in use is sufficient.

According to a fourth aspect of the present invention, in a magnetic bearing spindle device in which a spindle is supported by a plurality of sets of magnetic bearings in a non-contact manner, a rigidity characteristic measuring means for determining a relationship between a rotational speed of the spindle and rigidity, and the rigidity characteristic An optimal rotational speed selecting unit for selecting an optimal rotational speed from a measurement result of the measuring unit, wherein the rigidity characteristic measuring unit changes the rotational speed of the spindle stepwise within a predetermined rotational speed range, and Wherein the rigidity of the spindle is measured by a rigidity measuring means.

According to the fourth aspect of the invention, it is possible to measure the actual rigidity characteristics of the spindle in the use state and select an optimum rotational speed from the viewpoint of rigidity, and rotate the spindle at the optimal rotational speed. be able to.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the stiffness measuring means controls an exciting current supplied to the electromagnet of the magnetic bearing while the spindle is rotated at a predetermined rotation speed. Thus, the spindle is vibrated in a predetermined radial direction, a displacement of the spindle in the radial direction is measured, and a rigidity value of the spindle is calculated from the displacement.

In this case, as in the case of the second aspect of the present invention, there is no need to add a mechanical configuration for measuring the rigidity.
Then, means for changing the rotational speed of the spindle for measuring the rigidity characteristics and means for selecting the optimum rotational speed from the rigidity characteristics need only be added to the magnetic bearing control device as a program. There is no need to add a mechanical configuration for this.

According to the fifth aspect of the present invention, there is no need to add a mechanical configuration for measuring the rigidity characteristics and selecting the optimum rotation speed, and the configuration for measuring the rigidity characteristics and selecting the optimum rotation speed is added little. Help me.

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, a tool is mounted on a tip portion of the spindle, the magnetic bearing includes at least two sets of radial magnetic bearings, and the rigidity measuring means includes While rotating at a predetermined number of revolutions, the spindle is vibrated in a predetermined radial direction by controlling an exciting current supplied to the electromagnet of the radial magnetic bearing, so that the spindle at the position of each radial magnetic bearing is controlled. The method is characterized in that a displacement of the spindle in a radial direction is measured, and a rigidity value of the spindle at the tip of the tool is calculated from the displacement.

According to the sixth aspect of the present invention, there is no need to add a mechanical structure for measuring the rigidity characteristics and selecting the optimum rotational speed, as in the case of the fifth aspect of the present invention. Addition of a configuration for selecting the number is small. Also, by measuring the rigidity characteristics of the part of the tool mounted on the tip of the spindle, the optimum rotation speed can be selected from the viewpoint of rigidity, and the spindle can be rotated at the optimum rotation speed.

The invention of claim 7 is the invention of claim 4, 5 or 6
In the invention, the optimum rotation speed selecting means selects the rotation speed having the highest rigidity within the rotation speed range as the optimum rotation speed.

According to the seventh aspect of the present invention, it is possible to select a rotational speed having the highest rigidity within a predetermined rotational speed range and rotate the spindle at the rotational speed.

The invention of claim 8 is the invention of claim 4, 5 or 6.
In the invention, the optimum rotation speed selecting means selects the highest rotation speed among the rotation speeds within the rotation speed range and having a rigidity of a predetermined value or more as the optimum rotation speed. Is what you do.

According to the eighth aspect of the present invention, it is possible to select the highest rotational speed within a range having a certain degree of rigidity and to rotate the spindle at that rotational speed. The rotation speed does not become unnecessarily low.

[0036]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a magnetic bearing spindle device (1) used for a machine tool such as a machining center, and a numerical controller (hereinafter, referred to as a machine tool machining control means).
Abbreviated as “NC device”. 2) and an automatic tool changer (3) as an automatic tool changing means.

The spindle device (1) has a spindle (5) vertically arranged in a casing (4). In the casing (4), there is also provided a pair of axial magnetic bearings (6) for supporting the spindle (5) in a non-contact manner, and two upper and lower bearings.
A set of radial magnetic bearings (7), (8), one axial position sensor (9) for detecting the axial displacement of the spindle (5), and one for detecting the radial displacement of the spindle (5) Upper and lower two sets of radial position sensors (10) (11),
In addition, a high-frequency motor (12) is provided as a rotation driving means for rotating the spindle (5) at high speed. Usually, the axial magnetic bearing (6) is composed of a pair of electromagnets (6a), and each radial magnetic bearing (7) (8) is composed of four electromagnets (7a) (8a). In the following description, two radial axes orthogonal to each other will be referred to as an X axis and a Y axis, and an axial axis orthogonal to these axes will be referred to as a Z axis. In FIG.
As for the electromagnets (7a) (8a) of the radial magnetic bearings (7) (8) and the radial position sensors (10) (11), only those in the X-axis direction are shown. These magnetic bearings (6) (7) (8),
Since the position sensors (9), (10), and (11) are known, detailed description thereof will be omitted.

The axial position sensor (9) and the radial position sensors (10) and (11) are driven by a sensor drive circuit (13), and the sensor drive circuit (13) includes the position sensors (9), (10) and (1).
Based on the output of 1), the displacement of the spindle 5 in the axial direction (Z-axis direction) and two radial directions (X-axis direction and Y-axis direction) is detected. An analog position detection signal from the sensor drive circuit (13) is converted into a digital position detection signal by an A / D converter (14) and input to a magnetic bearing control device (15) as magnetic bearing control means. The magnetic bearing control device (15) controls the electromagnet (6a) of each magnetic bearing (6) (7) (8) based on the digital position detection signal, i.e., the axial and radial displacement of the spindle (5).
(7a) This is for controlling the magnitude of the exciting current supplied to (8a), and is composed of a DSP. The digital control signal from the magnetic bearing controller (15) is a D / A converter
(16) is converted to an analog control signal, and based on the analog control signal, the power amplifier (17) transmits each electromagnet (6
a) Excitation current is supplied to (7a) (8a), and as a result, the spindle (5) is attracted by the electromagnets (6a) (7a) (8a) and is supported at predetermined positions in the axial and radial directions without contact. You.

A tool (18) is mounted on the lower end of the spindle (5), and the tool (18) is changed to another type by an automatic tool changer (3) based on a tool number command from the NC device (2). It is designed to be automatically replaced with something. Since the automatic tool changer (3) is a known one, illustration and description of its specific configuration will be omitted. NC equipment
The tool number command from (2) is also input to the magnetic bearing control device (15).

The NC device (2) controls the position, the moving direction and the moving speed of the casing (4), that is, the spindle (5), thereby controlling the cutting depth and the feed speed of the tool (18). The NC device (2) is a spindle
(5) That is, a spindle rotation command for rotating the tool (18) is output to the magnetic bearing control device (15).

The magnetic bearing control device (15) includes a spindle
(5) Stiffness measuring means for measuring the stiffness, stiffness characteristic measuring means for obtaining the relationship (stiffness characteristic) between rotation speed and stiffness using the stiffness measuring means, and measurement results of the stiffness characteristic measuring means. An optimum rotation speed selecting means for selecting an optimum rotation speed is provided. That is, the DSP constituting the magnetic bearing control device (15) stores a software program constituting the rigidity characteristic measuring means and the optimum rotational speed selecting means. Next, an example of the measurement of the rigidity characteristics of the spindle (5) and the selection of the optimum rotational speed will be described with reference to the flowchart of FIG.

In FIG. 2, first, a lower limit rotation speed and an upper limit rotation speed of the spindle (5) for measuring rigidity characteristics are set (step 1). The lower and upper speed limits are:
For example, a lower limit value and an upper limit value of a usable maximum rotational speed range determined by the spindle device (1) can be set. Further, within the above-mentioned maximum rotation speed range, the lower limit value and the upper limit value of the usable rotation speed range determined by the tool (18) can be set as the lower limit rotation speed and the upper limit rotation speed, respectively. Next, the lower limit rotation speed is set to a rotation speed command value for rigidity characteristic measurement (step 2), and the motor (12) is started to start rotation of the spindle (5). Then, the rotation speed is controlled so that the rotation speed of the spindle (5) is maintained at the rotation speed command value (step 4).

If the rotation speed of the spindle (5) is held at the rotation speed command value, at the same frequency as the rotation speed at that time,
The spindle (5) is vibrated in one radial direction (X-axis direction in this example) (step 5). This is performed by controlling the exciting current supplied to a pair of electromagnets (7a) (8a) in the X-axis direction of the two sets of radial magnetic bearings (7) (8) as follows. The excitation current of the pair of electromagnets (7a) and (8a) is obtained by adding a control current controlled by the position of the spindle (5) in the X-axis direction to a constant steady current equal to each other. A sinusoidal control current having the same frequency as the rotation speed at that time and the same amplitude and a different phase by 180 degrees is supplied to each pair of electromagnets (7a) and (8a). At this time, the control current is controlled so that the direction and magnitude of the control current are always the same for the upper and lower electromagnets (7a) and (8a) on the same side in the X-axis direction with respect to the spindle (5). . On the other hand, the electromagnets in the Y-axis direction of the radial magnetic bearings (7) (8) and the electromagnets (6
In a), a constant steady current and a control current for holding the spindle (5) at a constant neutral position in the Y-axis direction and the Z-axis direction are supplied. This allows the upper and lower magnetic bearings (7)
In the portion (8), a load is applied in the X-axis direction which changes sinusoidally and has the same direction and magnitude at all times, and the spindle (5) is vibrated in the X-axis direction.
While the spindle (5) is vibrated in this manner, the radial position sensors (10) (11) in the X-axis direction and the sensor drive circuit (1) are driven.
Based on the output of 3), the displacement of the spindle 5 in the X-axis direction at the positions of the upper and lower radial magnetic bearings 7 and 8 is measured (step 6).

When the measurement of the displacement is completed, the rigidity value R of the spindle 5 at the tip end of the tool 18 in the X-axis direction is calculated (step 7). This operation is
This is performed using the following equation based on the principle shown in FIG.

R = (R1.L1 + R2.L2) / L In the above equation and FIG. 3, L is the distance from the center of gravity (G) of the entire spindle (5) (the combination of the spindle and the tool) to the position of the tool (18). Distance in the Z-axis direction to the tip, L1 is the center of gravity (G)
Distance in the Z-axis direction from the upper radial magnetic bearing (7) to
L2 is the Z from the center of gravity (G) to the lower radial magnetic bearing (8).
Axial distance. Since the position of the tip of the tool (18) and the positions of the upper and lower radial magnetic bearings (7) and (8) are constant, if the position of the center of gravity (G) is known, L, L1 and L2 can be determined. If the tool (18) changes, its weight also changes, so the center of gravity
The position of (G) also changes. The position of the center of gravity (G) is determined, for example, by using the electromagnets (6) (7) (8) of the magnetic bearings (6) (7) (8) when the spindle (5) is 6a) (7a) (8
It can be estimated from the excitation current in a). Therefore, when the tool (18) is changed, the center of gravity is
The position of (G) can be estimated and then L, L1 and L2 can be determined. Alternatively, when the tool (18) is determined, the position of the center of gravity (G) can be obtained by calculation or the like, so if the relationship between the tool number and the tool type is unchanged, each tool (18) was L, L1 and L2 at that time can be inputted to the magnetic bearing control device (15) and stored. R1 is the stiffness value at the position of the upper radial magnetic bearing (7). It is obtained as a ratio with the measured value of the displacement of. R2 is a stiffness value at the position of the lower radial magnetic bearing (8), which is obtained in the same manner as R1.

When the calculation of the stiffness value is completed, the rotational speed and the stiffness value of the spindle (5) at that time are stored (step 8). Then, it is checked whether or not the rotation speed command value at that time is equal to or higher than the upper limit rotation speed (step 9). If not, the process proceeds to step 10 to increase the rotation speed command value by a predetermined value. , And return to step 4. Step 10 and steps 4 to 9 are repeated until the rotation speed command value becomes equal to or higher than the upper limit rotation speed. When the rotation speed command value becomes equal to or higher than the upper limit rotation speed, the process proceeds from step 9 to step 11.

When the process proceeds to step 11, the measurement of the displacement and the calculation of the rigidity value when the spindle (5) is vibrated are performed for a plurality of rotation speeds between the lower limit rotation speed and the upper limit rotation speed. The processing is completed, and the stiffness value at each rotation speed is stored. In step 11, the optimum rotation speed is selected based on the relationship between the rotation speed and the rigidity value, and the process ends. When the processing is completed, the rigidity characteristics and the optimal rotation speed are stored in the magnetic bearing control device (15) together with the tool number. The optimum rotation speed can be set, for example, to the rotation speed having the highest rigidity value between the lower limit rotation speed and the upper limit rotation speed, or if the rigidity value is between the lower limit rotation speed and the upper limit rotation speed and is equal to or more than a predetermined value. It is also possible to set the highest rotation speed among certain rotation speeds. FIG. 4 shows the former example and FIG. 5 shows the latter example. FIG. 4 and FIG.
7 is a graph showing rigidity measurement results of two types of tools Nos. 1 and 2, that is, a relationship between a rotational speed (horizontal axis) and a rigidity value (vertical axis), where NL is a lower limit rotational speed, and NU is an upper limit rotational speed. . A indicates the measurement result for the tool of No. 1 and B indicates the measurement result for the tool of No. 2. In the case of FIG.
For each tool, the rotational speeds NA and NB having the highest rigidity values between the lower limit rotational speed NL and the upper limit rotational speed NU are the optimum rotational speeds. In the case of FIG. 5, RO is a stiffness value serving as a reference for selecting an optimum rotation speed.
The highest rotational speeds NA and NB among the rotational speeds having a rigidity value equal to or higher than RO and between the upper limit rotational speed NU and the upper limit rotational speed NU are the optimum rotational speeds.

In the above flow chart, the steps 4 to 8 constitute the rigidity measuring means, the steps 1 to 10 including the same constitute the rigidity measuring means, and the step 11 comprises the optimum rotational speed selecting means. In general machine tools, the relationship between the tool number and the type of tool is often unchanged. In such a case, the above-described rigidity characteristic measurement and optimal rotation speed selection need only be performed once for each tool at an arbitrary time point before machining with the tool. The optimum rotation speed selected for each tool is used for controlling the rotation speed of the spindle (5) when machining is performed by the tool. That is,
When receiving the spindle rotation command from the NC device (2), the magnetic bearing control device (15) rotates the spindle (5) at the optimum rotational speed stored for the tool corresponding to the tool number command at that time. The motor (12) is controlled as described above.

Even after the rigidity characteristic measurement and the selection of the optimum rotational speed are completed, if necessary, the optimum rotational speed of the same tool in a different rotational speed range may be selected for the same tool at any time during machining. You can also do. The selection of the optimum rotational speed is performed by, for example, the
This is performed by designating and issuing a new rotational speed range (a range narrower than the initial range) from (2). At this time, since the rigidity characteristic of the tool is stored in the magnetic bearing control device (15), the rigidity characteristic measurement is not performed, and only the optimal rotational speed selection for the new rotational speed range is performed in the same manner as described above. it can.

The selection of the optimum rotation speed for each tool can be performed only after the rigidity characteristic measurement for the same tool is completed. However, the timing of the rigidity characteristic measurement and the selection of the optimum rotation speed, and the machining time based on these results, Regarding the method of controlling the number of revolutions of the spindle (5), various modes other than the above can be considered.

In the above example, the rotation speed is controlled based on the optimum rotation speed stored in the magnetic bearing control device (15). However, the optimum rotation speed is stored in the NC device (2), May be output to the magnetic bearing control device (15) to control the rotation speed.

Step 1 in the flowchart of FIG.
The part corresponding to the stiffness characteristic measurement of ~ 10 is a magnetic bearing control device
The step (15) may be performed, and the portion corresponding to the selection of the optimum rotational speed in step 11 may be performed by the NC device (2). Alternatively, only the portion corresponding to the rigidity measurement in steps 4 to 8 may be performed by the magnetic bearing control device (15), and the remaining portion may be performed by the NC device (2).

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a magnetic bearing spindle device showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an example of rigidity characteristic measurement and optimal rotation speed selection.

FIG. 3 is an explanatory diagram illustrating the principle of rigidity value calculation.

FIG. 4 is a graph showing an example of rigidity characteristics and selection of an optimum rotation speed.

FIG. 5 is a graph showing another example of rigidity characteristics and selection of an optimum rotation speed.

[Explanation of symbols]

 (1) Magnetic bearing spindle device (5) Spindle (6) Axial magnetic bearing (6a) Electromagnet (7) (8) Radial magnetic bearing (7a) (8a) Electromagnet (9) Axial position sensor (10) (11) Radial Position sensor (12) High frequency motor (15) Magnetic bearing control device

Claims (8)

[Claims] 1. A magnetic bearing spindle device in which a spindle is supported by a plurality of sets of magnetic bearings in a non-contact manner, comprising a rigidity measuring means for measuring rigidity of the spindle. 2. The apparatus according to claim 1, wherein said stiffness measuring means controls an exciting current supplied to an electromagnet of said magnetic bearing in a state where said spindle is rotated at a predetermined number of revolutions, thereby exciting said spindle in a predetermined radial direction. 2. The magnetic bearing spindle device according to claim 1, wherein a displacement of the spindle in the radial direction is measured, and a rigidity value of the spindle is calculated from the displacement. 3. A state in which a tool is mounted on a tip of the spindle, the magnetic bearing includes at least two sets of radial magnetic bearings, and the stiffness measuring means rotates the spindle at a predetermined number of revolutions. By controlling the exciting current supplied to the electromagnet of the radial magnetic bearing, the spindle is excited in a predetermined radial direction, and the displacement of the spindle in the radial direction at the position of each radial magnetic bearing is measured. 2. The magnetic bearing spindle device according to claim 1, wherein a rigidity value at a tip of the tool of the spindle is calculated from the displacement. 4. In a magnetic bearing spindle device in which a spindle is supported by a plurality of sets of magnetic bearings in a non-contact manner, rigidity measuring means for determining a relationship between the rotational speed and rigidity of the spindle, and measurement results of the rigidity measuring means. Optimal rotational speed selecting means for selecting an optimal rotational speed from the above, wherein the rigidity characteristic measuring means changes the rotational speed of the spindle stepwise within a predetermined rotational speed range, and the rigidity measuring means at each rotational speed. A magnetic bearing spindle device for measuring the rigidity of the spindle. 5. The stiffness measuring means controls the exciting current supplied to the electromagnet of the magnetic bearing in a state where the spindle is rotated at a predetermined number of revolutions, thereby exciting the spindle in a predetermined radial direction. 5. The magnetic bearing spindle device according to claim 4, wherein a displacement of the spindle in the radial direction is measured, and a rigidity value of the spindle is calculated from the displacement. 6. A state in which a tool is mounted on a tip of the spindle, the magnetic bearing includes at least two sets of radial magnetic bearings, and the stiffness measuring means rotates the spindle at a predetermined number of rotations. By controlling the exciting current supplied to the electromagnet of the radial magnetic bearing, the spindle is excited in a predetermined radial direction, and the displacement of the spindle in the radial direction at the position of each radial magnetic bearing is measured. 5. The magnetic bearing spindle device according to claim 4, wherein a rigidity value at a tip of the tool of the spindle is calculated from the displacement. 7. The optimum rotation speed selecting means for selecting the rotation speed having the highest rigidity within the rotation speed range as the optimum rotation speed.
Magnetic bearing spindle device. 8. The optimum rotation speed selecting means selects the highest rotation speed among the rotation speeds within the rotation speed range and having a rigidity equal to or higher than a predetermined value as the optimum rotation speed. 7. The magnetic bearing spindle device according to claim 4, 5 or 6.