Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-12-11
2004-10-26
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C318S607000
Reexamination Certificate
active
06809449
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a controller for a magnetic bearing in an apparatus using the magnetic bearing as a means for supporting a rotor, and more particularly to a controlled magnetic bearing apparatus suitable for suppressing a vibration amplitude in accordance with a whirling movement of an unbalanced rotor.
BACKGROUND ART
FIG. 1
shows a basic configuration of a conventionally typical controlled magnetic bearing apparatus having a feedback control system. For easy understanding, in an illustrated example, a part of a bearing apparatus for radially supporting a rotating shaft
1
has been extracted and is designed to control a vibration amplitude of the rotor
1
in an X-axis direction on an X-Y plane (transverse plane) perpendicular to the rotating shaft
1
. Specifically, in
FIG. 1
, the horizontal axis is taken in an X-axis direction, and the vertical axis in a Y-axis direction, about a center of the rotor
1
. Displacement sensors
2
a
,
2
b
, and electromagnets
3
a
,
3
b
are disposed on the X-axis with interposing the rotor
1
therebetween. An electric current to be supplied to the electromagnets
3
a
,
3
b
is controlled based on sensor signals from the displacement sensors
2
a
,
2
b
. Electromagnets and displacement sensors are similarly disposed on the Y-axis with interposing the rotor
1
therebetween, and an electric current is controlled in the same manner.
As shown in
FIG. 1
, the displacement sensors
2
a
,
2
b
, which are disposed on the X-axis with interposing the rotor
1
therebetween, and which detect radial displacements of the rotating shaft
1
, are connected to a sensor amplifier
4
. The displacement sensors
2
a
,
2
b
and the sensor amplifier
4
constitute a displacement sensor unit. An output signal from the sensor amplifier
4
is an electric signal (sensor signal) corresponding to a displacement of the rotor
1
in the X-axis direction. The sensor signal is inputted into a first control unit
5
for generating a compensation signal utilized for holding the rotor
1
at a desired levitating position.
The first control unit
5
calculates first control signals based on the sensor signal and outputs the first control signals as control currents. The control signals (control currents) are amplified by power amplifiers
6
a
,
6
b
respectively connected to the electromagnets
3
a
,
3
b
, and then supplied to coils of the electromagnets
3
a
,
3
b
. In each of the electromagnets
3
a
,
3
b
, an electromagnetic force is generated by the electric current supplied to each of the coils of the electromagnets
3
a
,
3
b
. The rotor
1
is magnetically attracted to the electromagnets
3
a
,
3
b
by the electromagnetic forces. Thus, in accordance with a displacement of the rotor
1
in the X-axis direction, the control currents are supplied to a pair of the electromagnets
3
a
,
3
b
disposed at an opposite position to each other on the X-axis, and hence the rotor
1
is servo controlled so as to be held in a levitated state at a central position or a target position by the attracting forces of the electromagnets
3
a
,
3
b.
When applications of magnetic bearings become wider, the following problems may arise because of restrictions on their structure, size, and the like:
For example, when a largely unbalanced rotor is rotated while being radially supported by a magnetic bearing, eccentric rotation of the rotor, i.e., whirling, may occur. In such a case, if the degree of eccentricity of the rotor becomes large, then the whirling range of the rotor cannot be within a touchdown gap of the magnetic bearing. Consequently, the rotor cannot be supported in a non-contact levitated state, and this may damage the device.
Further, In the event that a rotor is not levitated at a magnetic center of a motor stator, an external force synchronized with a rotational movement of the motor acts on the rotor. Particularly, in the case of a machine working upon rotation, e.g., a blower, since a load is increased due to an increasing rotational speed, a motor output needs to be increased, and a greater external force synchronized with the rotational movement of the motor acts on the rotor. Consequently, the rotor whirls considerably, and hence a touchdown may occur depending on the degree of the whirling.
Furthermore, when a radial electromagnetic force synchronized with a rotational movement of a motor is generated, a force acting on a rotor as an external force becomes a great load, regardless of a levitating position of the rotor. In this case, as in the aforementioned case, the rotor whirls considerably, and hence a touchdown may occur depending on the degree of the whirling.
In any of the cases, the application of a bearing that can produce a sufficient control power on an external force would solve the problems. However, a stiffness of a magnetic bearing is smaller than that of a rolling bearing or a sliding bearing. Thus, it is difficult for a magnetic bearing to have a stiffness equivalent to that of a rolling bearing or a sliding bearing. For example, when a magnetic flux density of 1 tesla is generated in a space where areas of 1 square centimeter are opposed to each other, an obtained attracting force is about 40 newtons as Maxwell's stress equation shows. With a controlled magnetic bearing, since a magnetic flux density is generally about 0.5 tesla, an attracting force of only about 10 newtons is obtained.
Accordingly, it has recently been attempted to adopt a feed forward control in which an external force synchronized with a rotational movement of a rotor is estimated, and an input with the addition of a control signal for canceling out the estimated external force is inputted into a power amplifier to thus suppress whirling of the rotor. Further, there has been known an open balance control in which a sine wave or a triangular wave signal synchronized with a rotational speed of a rotor is added to a known external force, and the sum is inputted into a power, amplifier to thus control whirling of the rotor. These types of control require not only sensor signals from the displacement sensors
2
a
,
2
b
disposed with interposing the rotor
1
therebetween as shown in
FIG. 1
, but also sensor signals from a displacement sensor for detecting displacements of the rotor
1
in the axial direction of the rotor
1
, and pulse signals synchronized with the rotational movement of the rotor
1
.
DISCLOSURE OF INVENTION
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a controlled magnetic bearing apparatus which generates a control signal based on a sensor signal from a displacement sensor for detecting a radial displacement of a rotor to suppress whirling of the rotor due to an external force synchronized with a rotational movement, and can hence support the rotor stably in a levitated state.
A voltage signal proportional to a rotational speed, which is obtained from an existing motor controller, is used either for turning on and off a signal switch before a control signal is inputted into a power amplifier, or for operation of a rotational speed component extraction filter.
According to claim
1
of the present invention, there is provided a controlled magnetic bearing apparatus for radially supporting a rotor, comprising a displacement sensor for detecting a radial displacement of the rotor, a first control unit for calculating a first control signal based on a sensor signal from the displacement sensor and outputting the first control signal, a power amplifier for supplying an electric current based on the first control signal, and an electromagnet for generating a magnetic force based on a signal from the power amplifier, the controlled magnetic bearing apparatus further comprising: a second control unit disposed in parallel with the first control unit for generating a second control signal changed in phase from the sensor signal inputted therein and outputting the second control signal; and a signal synthesizer for adding the second cont
Ebara Corporation
Waks Joseph
Westerman Hattori Daniels & Adrian LLP
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