Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1995-03-17
2001-03-27
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S090000
Reexamination Certificate
active
06208051
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spindle apparatus and, more particularly, to a spindle apparatus using a magnetic bearing. In some spindle apparatus, in order to realize a super high speed rotation, or a long term non-maintenance or the like, a magnetic bearing is leviated floated without any contact with a rotary shaft (i.e., rotary body) by a magnetic force. The magnetic bearing is so constructed that an output of a positional shift sensor for detecting a position of the rotary shaft is fed back to control an excited current of an electromagnet and to control the floating position of the rotary shaft. In this feedback operation, if an imbalance (offset between an axial center and a gravitational center) is present in the rotary shaft, a magnetic force which is in synchronism with a rotary frequency (i.e., rpm) is generated in order to suppress a vibratory rotation of the rotary shaft which is generated due to the imbalance. Accordingly, when the rotary frequency is equal to a natural frequency (resonant frequency), the rotary shaft is resonated by the magnetic force of the magnetic bearing, as a result of which, in particular, in a high speed rotational region, the rotary shaft is deformed to cause a bending vibration.
FIG. 3
shows a state in which a rotary shaft
10
that is floatingly held by a magnetic bearing is subjected to the bending vibration as indicated by dotted lines with nodes at points A and B.
As shown in
FIG. 3
, the rotary shaft
10
is supported at both ends thereof by four electromagnets
12
,
14
,
16
and
18
. The positional shift in a radial direction of the rotary shaft
10
is detected by positional shift sensors
20
,
22
,
24
and
26
. In general, in the bending vibration, the nodes of the vibration are generated in the vicinity of both ends of the shaft, and also, the support positions of the magnetic bearing, i.e., the electromagnets are located in the vicinity of both ends of the shaft. Accordingly, as shown in
FIG. 3
, the nodes of the vibration (points A and B) are located in the vicinity of the electromagnets.
Usually, a circuitry or the like for phase compensation on the basis of a PID control (proportional-integral-derivative control) is incorporated into a control circuit for controlling the excited current of the electromagnets in the magnetic bearing. In order to suppress the resonant vibration, an electric damping is applied by using the magnetic force of the electromagnets and the current in the vicinity of the resonant frequency is interrupted by using a filter.
Also, in the prior art, a mechanical damper made of rubber material has been used at a portion C which is a middle portion in the vibration of the rotary shaft
10
, thereby suppressing the generation of the bending vibration.
However, as shown in
FIG. 3
, if the points A and B that are the nodes of the vibration are located at the vicinity of mount positions of the respective electromagnets
12
,
14
,
16
and
18
, the magnetic force of the electromagnets is not applied to the rotary shaft
10
as a force for suppressing the vibration. Accordingly, in the electric damping control using the above-described compensation circuit and the like, it is impossible to suppress the generation of the resonance. Also, in the case where the current in the vicinity of the resonance frequency is interrupted by using the filter, a rigidity of the magnetic bearing is degraded so that the rotary shaft
10
per se is likely to be vibrated by disturbance.
With the mechanical damper, it is possible to suppress the vibration of the middle portion C, but in this case, it is impossible to actively suppress the bending vibration unlike with the electric damping control. Also, the mechanical damper also suffers from a problem in durability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spindle apparatus which is capable of preventing the bending vibration of a rotary shaft.
In order to attain the foregoing object, according to the present invention, there is provided a spindle apparatus comprising: a rotary shaft; a first magnetic bearing for floatingly holding one end end of the rotary shaft by magnetic forces; a second magnetic bearing for floatingly holding another end side of the rotary shaft by magnetic forces; and a magnetic bearing composite motor interposed between the first magnetic bearing and the second magnetic bearing, the magnetic bearing composite motor having a magnetic bearing function for positionally controlling the rotary shaft by the magnetic forces and a motor function for imparting a rotational torque to the rotary shaft by the magnetic forces.
In such a spindle apparatus, the rotary shaft is rotated by the magnetic bearing composite motor and simultaneously the magnetic forces are applied to a portion of the rotary shaft between the first and second magnetic bearings to perform the positional control of the rotary shaft.
REFERENCES:
patent: 4642500 (1987-02-01), Higuchi et al.
patent: 4686004 (1987-08-01), Nakazeki et al.
patent: 4841204 (1989-06-01), Studer
patent: 4885491 (1989-12-01), Hiyama et al.
patent: 5053662 (1991-10-01), Richter
patent: 5093754 (1992-03-01), Kawashima
patent: 5313399 (1994-05-01), Beale
patent: 5355042 (1994-10-01), Lewis et al.
patent: 5469007 (1995-11-01), Toyama
patent: 0291931 (1988-11-01), None
patent: 0315469 (1989-05-01), None
Patent Abstract of Japan, vol. 11, No. 11 (E-470) Jan. 13, 1987.
VDI Zeitschrift, vol. 132, No. 12, Dec. 1990, Dusseldorf, Germany, pp. 77-79, V. W. Horsemann, “Prozebregelung beim Innernrundschleifen mit aktiv magnetelagerten Spindeln” .
Adams & Wilks
Enad Elvin
Seiko Seiki Kabushiki Kaisha
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