Hardware Reference
In-Depth Information
0.12
0.1
0.08
0.06
0.04
0.02
0
0
500
1000
1500
2000
2500
3000
Frequency [Hz]
Figure 3.62: Linear spectrum of PES after disk vertical vibration feedforward
compensation.
Table 3.5: The amplitude of dominant modes in PES spectrum before and
after compensation.
Frequency
Magnitude before
Magnitude after
Reduction
(Hz)
compensation (mVrms)
compensation (mVrms)
%
504
33.1
11.2
66
598
40.3
22.5
44
648
73.9
23.9
68
696
100.9
52.0
48
1018
30.0
25.1
16
as input to the basic servo loop and reduced the TMR induced by the first four
disk flutter modes by 56%.
The method presented here requires a vertical vibration sensor, and there-
fore, increases the cost when implemented in a commercial HDD. However, this
technique can be used in applications whereby precision positioning is required
and the extra sensor can be reused. For example, the method can be used to
improve the positioning accuracy in the testing equipments such as servo track
writers or spinstands to reduce the written-in runout. Development of various
technologies such as MEMS will eventually bring the cost down and measure-
ment of the vertical vibration will be a practical solution that cen be applied
in HDD. Additionally, the same instrumented suspension for expanding the
servo bandwidth and reducing the suspension vibrations (all in the in-plane
direction) might also be used for measuring the vertical direction vibration for
