Hardware Reference
In-Depth Information
used to
fi
lter out the noise in the amplitude noise.
Figure 5.11: Schematic of an imbalance measurement machine with
fl
exible
bearing.
Let the output signal of the bandpass
fi
lter be represented by V
f
e
jδ
,which
means that it has an amplitude V
f
and phase δ with reference to the motor
index measured by a tachometer. To calibrate the amplitude and phase of the
machine,
fi
rst, the amplitude and phase of the disk-spindle pack imbalance is
read, and its value is represented by V
1
.Nextaknownmassw gram is placed
at 0 angle at radius R mm with respect to the motor index mark, the imbalance
reading is represented by V
2
. The calibration vector
V
3
= V
2
−V
1
= V
3
e
jγ
where V
3
and γ are the amplitude and angle of the calibration vector respec-
tively.
The actual imbalance I
m
will be
I
m
= V
f
wR
V
3
e
δ−γ
.
If we have the knowledge of the imbalance in disk-spindle pack, the imbal-
ance can be corrected by adding or removing equivalent amount of mass. A
spacer ring with 24 screws of known masses is used. By adjusting the screw's
radial distance to the center of rotation, a
fi
ne change in center of gravity can
be in
fl
icted and hence the imbalance can be corrected. Interested readers may
refer to [86], [87], [217] and the references therein for more discussions on the
balancing techniques.
5.5.3 Control System
The control block diagram is shown in Figure 5.12. Let P
1
(s)betheMicroE
arm model, C
1
(s) be the controller available in the MicroE, K(s)bethemodel
