JPH04203523A - Magnetic bearing spindle - Google Patents

Abstract

PURPOSE:To improve the precision and rigidity by setting the gap between a spindle and a protecting bearing to ten times of the aimed precision and setting the sensitivity of the amplification circuit of a controller to the max value with which the circuit is not saturated, even if the spindle is shifted to any position within the gap. CONSTITUTION:A protective bearing is a ceramic slide bearing made of the heat-resistive and abrasionproof material both in the radial and thrust directions. The gap of the protective bearing is set to about ten-times to the aimed precision. At this time, the position of the spindle is shifted within the gap of the protective bearing at the U-point, and if a circuit is not yet saturated, each frequency f0, f1, f2 is shifted to the higher value, while if the circuit is saturated, the frequency is lowered, and the value of the degree K of amplification is adjusted to the limit less than the saturation point. The gap of the protecting bearing is reduced, and the rigidity is improved drastically by setting the degree of amplification of a control circuit to the max. value which is less than the saturation value even after the spindle shifts within this range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a magnetic bearing spindle whose performance is improved by improving the protective bearing.

(Prior Art) A protective bearing is attached to an active magnetic bearing in order to cope with an unexpected accident such as a failure of a control device or an excessive disturbance.

A rolling bearing is used as the protective bearing, and the clearance between the rolling bearing and the shaft is from 0.1 m to about 1.0 m in some cases, which is extremely wide for a bearing. In order for this to work as a spindle, it is necessary to ensure that the rolling bearing of the protective bearing can support the shaft in an unexpected situation, and that the shaft does not come into contact with the protective bearing during normal operation, from a safety standpoint. The value is like this.

The gap between the rotor and stator of the electromagnets constituting the magnetic bearing is further widened so that even if the protective bearing comes into contact with it, it will not hit.

(Problem to be Solved by the Invention) With a wide gap as in the above-mentioned conventional technology, it is not possible to increase the sensitivity of the sensor (voltage amplification degree of the amplifier circuit) that detects the position of the axis. This is because if the amplification degree of the control circuit is increased, if the axis position deviates even slightly from the setting, the amplification circuit will quickly become saturated and control will become impossible.

For this reason, even if the position of the shaft changes over the entire area within the gap, the degree of amplification can only be increased to a level that does not saturate, and as a result, the bearing performance, particularly the accuracy and rigidity of the bearing, cannot be improved. For this reason, it was insufficient for applications that require precision and rigidity of the spindle, such as spindles for machine tools.

The present invention improves the type, structure, and material of the protective bearing to narrow the allowable clearance as much as possible, thereby increasing the sensitivity of the amplifier circuit, and increasing the accuracy and rigidity of the magnetic bearing spindle. It is.

(Means for Solving the Problems) Therefore, the present invention has solved the problems of the prior art by providing a magnetic bearing spindle as set forth in the claims.

(Example) An embodiment of the present invention is shown in FIGS. 1 to 3.

In the figure, 1 is the main shaft of the spindle, 2 is the outer cylinder, 3 is the motor that drives the main shaft, 4 is the radial magnetic bearing on the spindle head side, 5 is the radial magnetic bearing on the spindle tail side, 6 is the thrust magnetic bearing, 7 and 8 9 is a sensor that detects the axis position in each radial direction, 9 is a front cover of the spindle, 1 is
0 also indicates the rear lid.

The protective bearing used here is a ceramic sliding bearing made of heat-resistant and wear-resistant material in both the radial and thrust directions, and is designed to withstand contact during high-speed rotation of the main shaft.

At the location where the main shaft 1 passes through the front cover 9, a protective bearing on the spindle head side is provided, as shown in detail in FIG. A ceramic protective bearing stator 12 is fitted and fixed on the front cover 9, and a ceramic protective bearing rotor 1 is mounted on the main shaft 1 opposite to this.
1 is fitted and fixed. Since it is necessary to particularly increase the rigidity of the magnetic bearing on the spindle head side, the gap between the rotor 11 and the stator 12 in the protective bearing is set to 10 μm. Note that 13 is a front cover that covers the protective bearing portion, and 14 is a sleeve that is fitted onto the main shaft and serves as a sensor target. The details of the protective bearing on the spindle tail side are shown in FIG. 3. A ceramic protective bearing stator 16 is attached to a mounting ring 15 fixed to the inner diameter side of the outer cylinder 2 adjacent to the stator of the thrust magnetic bearing. It is firmly fitted and secured, and is prevented from being removed by a retaining ring 18. Protective bearing stator 1
A protective bearing rotor 17 made of ceramic is fitted and fixed to the main shaft 1 opposite to the rotor 6 . A ceramic collar 19 adjacent to the inner end of the protective bearing rotor 17 to counter the thrust is fitted and fixed to the main shaft, and a ceramic collar 19 adjacent to the end of the protective bearing rotor 17 to counter the thrust in the opposite direction is fitted and fixed to the main shaft. A collar 20 is fitted onto the main shaft and fastened and fixed with a double nut 22 via a rotor disk 21 of a thrust magnetic bearing. In addition, 2
3 is a stator of the thrust magnetic bearing. Each clearance of the protective bearing on the spindle tail side is 100 μm between the rotor 17 and stator 16, between the stator 16 and collar 19, and between the stator 16 and collar 20.
, which is larger than the gap on the spindle head side.

The control circuit is a general PDI type feedback control as shown in Fig. 4, and the overall frequency characteristics from the sensor amplifier to the current amplifier are composed of a proportional circuit P, a differential circuit D,
When integrating circuit I is energized with a suitable amplification factor, characteristics as shown in FIG. 5 are obtained. In Fig. 5, if the frequency at the intersection of the ■ component and the P component is f, the frequency at the intersection U between the P and D components is fl, and the frequency at the upper limit point V of the D component is ft, then P
The component gives stiffness, and the D component gives damping ('$i damping). Therefore, in order to obtain sufficient damping at point U, the frequency f2 at point ■ should be set to 10 times the frequency at point U, f. Set it at a certain level. If the 7 point is high, the damping will be good, but the whole circuit will become unstable. Furthermore, if the ■ point is too low, no damping effect can be obtained. When a sensor and an electromagnet are connected to a control circuit with such characteristics to form a feed bank loop and actively hold the spindle main shaft, the block diagram of the entire system is shown in Fig. 6.
It will look like the figure. Here, So, Sr%Sz are the frequencies f in FIG. 5, respectively. ,f,,f.

is the value in Laplace space equivalent to . Disturbance or rotational error
When is input, feedback works to make this X' to zero for the entire system, but it is completely
Assuming that it does not become 0 but has now converged to the value of X, the value of By appropriately determining the amplification degree K in relation to ro, 1, f2, and mass M, the frequency characteristics of the disturbance correction amount can be set as shown in FIG. That is, at the intended frequency of V, there is no ability to correct the error at all, and at the tJ point, the setting is made so that the error can be compressed to about 1/10. Therefore, in order to realize a spindle with a rotation accuracy of 1 μm, first the accuracy of the sensor target should be set to about lum to achieve a good balance.

This guarantees an error of 1 μm at frequencies of 7 or more points. Since an error of up to 10 μm is allowed at point U, the gap between the protective bearing as a touchdown bearing is set to 10 μm. This is the reason why the gap between the protective bearings is set to about 10 times the target accuracy. At this time, try moving the position of the main shaft within the gap between the protective bearings at point U, and if the circuit is not yet saturated, move the values of fo, f, and ft to a higher value, and vice versa. If you end up doing it, fo, ft,
Lower the value of ft and adjust the value of K to a limit that does not reach the saturation point.

In the present invention, the rigidity has been significantly improved by narrowing the gap between the protective bearings to 10 μm and setting the amplification degree of the control circuit to the maximum value that does not saturate even if the main shaft is displaced within this 10 μm range.

Figure 8 shows a comparison between a conventional active magnetic bearing and this one. Generally, the stiffness of magnetic bearings has frequency characteristics. The most important thing is the minimum value of dynamic stiffness, not static stiffness.The best data for the conventional model was that the minimum value of dynamic stiffness was 100 gf/μm, but the one of the present invention has IKg
Slightly exceeds f/μm.

Regarding accuracy, the accuracy at low speed rotation has been significantly improved. FIG. 9 shows a comparison between the present invention and the conventional one using two resurge waveforms. However, the problem is that the accuracy of the sensor target directly appears, and the vibration of the outer cylinder increases at high speed rotation. This is another problem that should be addressed by improving the processing accuracy of the target.

(Effects of the Invention) In the present invention, the protective bearing of the magnetic bearing spindle is a heat-resistant and wear-resistant ceramic sliding bearing, the gap between the main shaft and the protective bearing is set to about 10 times the target accuracy, and the control device is amplified. Since the sensitivity of the circuit is set to the maximum value at which the circuit will not become saturated no matter what position the spindle is displaced within the gap, it is possible to set the bearing gap during operation of the magnetic bearing spindle to be extremely narrow, and Accordingly, the accuracy and rigidity of the spindle main shaft can be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an embodiment of the present invention, Fig. 2 is an enlarged view of the part ■ in Fig. 1, Fig. 3 is an enlarged view of the m part in Fig. 1, and Fig. 4 is a control circuit. 5 is a graph showing the frequency characteristics of the amplification degree of the control circuit, FIG. 6 is a block diagram of the entire system, and FIG. 7 is a graph showing the frequency characteristics of the error correction amount in the entire system. FIG. 8 is a graph showing a comparison between the present invention and the prior art regarding the frequency characteristics of the rigidity of a magnetic bearing, and FIG. 9 is a comparison diagram of surge waveforms. 1...Main shaft, 2...Outer cylinder, 3...Motor, 4.5
...Radial magnetic bearing, 6...Thrust magnetic bearing,
7.8... Sensor, 11.17... Protective bearing rotor, 12.16... Protective bearing stator, 1
9.20...Protective bearing collar. Agent Patent Attorney Jun Kawachi Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Sa number [H2] -- Mllll number box diagram of control circuit Figure 7 llI2! number (Hzl - Local wave number characteristics of disturbance correction amount Figure 8 1 10 100
+ KMJI number [Hz Coco-air bearing stiffness Ma number time characteristic 9WJ 2 ) rm /div 2 pm/d
iv (A) Magnetic bearing according to the present invention (B)
Rotational accuracy due to conventional magnetic bearing Lissurge dual waveform

Claims (1)

[Claims] A motor that rotates the spindle, an active magnetic bearing that supports the spindle without contact, a control device that controls the position of the spindle in the active magnetic bearing, and a motor that contacts the spindle when the spindle position becomes uncontrollable. In a magnetic bearing spindle equipped with a protective bearing that supports the spindle, the protective bearing is a heat-resistant and wear-resistant ceramic sliding bearing, and the gap between the main shaft and the protective bearing is about 10 times the target accuracy,
A magnetic bearing spindle, characterized in that the sensitivity of the amplifier circuit of the control device is set to a maximum value at which the circuit does not become saturated no matter what position the main shaft is displaced within the gap.