Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-09-07
2002-06-11
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R
Reexamination Certificate
active
06404088
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic bearing device for levitating an object in an arbitrary position out of contact with electromagnets under magnetic attractive or repulsive forces generated by the electromagnets.
2. Description of the Related Art
FIG. 1
of the accompanying drawings shows a conventional magnetic bearing device. As shown in
FIG. 1
, the conventional magnetic bearing device comprises a magnetizable object
105
to be levitated, a pair of electromagnets
101
,
102
for generating magnetic forces to levitate and support the object
105
, and a pair of positional displacement sensors
103
,
104
for detecting a positional displacement of the object
105
. The object
105
is disposed between the electromagnets
101
,
102
and also between the positional displacement sensors
103
,
104
.
The object
105
is subject to electromagnetic attractive or repulsive forces generated by the electromagnets
101
,
102
. The electromagnetic attractive or repulsive forces generated by the electromagnets
101
,
102
are compensated for by a control circuit based on a detected positional displacement signal produced by the positional displacement sensors
103
,
104
. The object
105
is levitated and supplied under the electromagnetic attractive or repulsive forces generated by the electromagnets
101
,
102
.
The control circuit
111
comprises a sensor circuit
110
, a compensating circuit
108
, and a driver
109
. The sensor circuit
110
comprises an offset corrector
106
and a sensor gain adjuster
107
.
The detected positional displacement signal produced by the positional displacement sensors
103
,
104
is compared with a threshold level preset in the sensor circuit
110
, and a differential signal is compensated for by the compensating circuit
108
to control the driver
109
to apply drive signals to the electromagnets
101
,
102
so as to levitate and support the object
105
in a desired position between the electromagnets
101
,
102
.
The threshold level is preset so as to be substantially equal to the detected positional displacement signal produced by the positional displacement sensors
103
,
104
when the object
105
is positioned at the center of a levitation range between the electromagnets
101
,
102
. The driver
109
energizes the electromagnets
101
,
102
to levitate and support the object
105
so as to minimize the differential signal between the threshold level and the detected positional displacement signal.
In order to preset the threshold level, it has heretofore been customary to manually move the object
105
or move the object
105
under magnetic forces from the electromagnets
101
,
102
, in a mechanically movable maximum range between the electromagnets
101
,
102
. The offset corrector
106
calculates a middle value of the detected positional displacement signal from maximum and minimum values of the detected positional displacement signal which are produced by the positional displacement sensors
103
,
104
when the object
105
is thus moved. The calculated middle value is used as the threshold level or zero point.
If the magnetic bearing device is very large or very long or if the object
105
to be levitated cannot be touched, then it is practically impossible to move the object
105
manually in the mechanically movable maximum range between the electromagnets
101
,
102
.
Adjusting the levitated position of the object
105
under magnetic forces produced by the electromagnets
101
,
102
also needs special care. Specifically, if the positional displacement sensors
103
,
104
have inaccurate output characteristics due to mechanical dimensional errors or individual variations of the positional displacement sensors
103
,
104
, or either the magnetic bearing mechanism or the control circuit
111
is replaced at the time of maintenance of the magnetic bearing device, then it is necessary to adjust the levitated position of the object
105
in the magnetic bearing mechanism with the control circuit
111
to be used in a new combination.
The magnetic bearing device has auxiliary supports (auxiliary bearings) for contacting and supporting the object
105
in case the object
105
is held at rest while being levitated or the levitation control process suffers a malfunction. If the auxiliary supports are damaged, broken or excessively worn to the extent that they fail to perform their own function, then such a failure cannot be detected while the magnetic bearing mechanism remains assembled.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic bearing device which makes it easy to adjust a preset level for the levitated position of an object to be levitated and which is capable of easily detecting deformation or wear of an auxiliary support for the object to be levitated.
To achieve the above object, there is provided a magnetic bearing device comprising a pair of electromagnets, a magnetizable object to be levitated which is disposed between the electromagnets, a pair of positional displacement sensors for detecting a positional displacement of the object, and a control circuit responsive to a detected positional displacement signal from the positional displacement sensors, for outputting a control current to control magnetic attractive or repulsive forces produced by the electromagnets to levitate the object in an arbitrary position between the electromagnets out of contact therewith, the control circuit comprising offset correcting means for producing an offset-corrected signal from the detected positional displacement signal from the positional displacement sensors, position compensating means for compensating for the offset-corrected signal from the offset correcting means, a driver responsive to a compensated signal from the position compensating means for applying a drive signal to energize the electromagnets, control means for controlling the driver to successively energize the electromagnets to move the object in a mechanically movable maximum range between the electromagnets, detecting maximum and minimum values of the detected positional displacement signal from the positional displacement sensors, calculating a middle value between the maximum and minimum values, and comparing the middle value with a predetermined threshold level, and output adjusting means for adjusting the offset-corrected signal from the offset correcting means to substantially eliminate the difference between the middle value and the threshold level so that the middle value represents a position in which the object is to be levitated between the electromagnets.
The control circuit may further comprise means for selectively entering a manual or automatic setting process command to perform a process of controlling said control means to control said driver to successively energize said electromagnets to move said object in a mechanically movable maximum range between said electromagnets, detect maximum and minimum values of the detected positional displacement signal, calculate the middle value between said maximum and minimum values, and compare said middle value with a predetermined threshold level, and said output adjusting means to adjust the offset-corrected signal to substantially eliminate the difference between said middle value and said threshold level.
The magnetic bearing device may further comprise a pair of auxiliary supports for limiting a movable range of the object, and the control circuit may further comprise means for monitoring a change in the maximum and minimum values of the detected positional displacement signal when the object is moved in the mechanically movable maximum range between the electromagnets, thereby to detect when the auxiliary supports suffer a failure.
By successively energizing the electromagnets, the object is moved in the mechanically movable maximum range between the electromagnets. At this time, maximum and minimum values of the detected positional displacement signal from the positional dis
Barada Toshimitsu
Nakazawa Toshiharu
Ooyama Atsushi
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