Figure 3.55: Shock transfer function of servo system.
the four modes also appear in Figures 3.57. However, the modes above 2 kHz
seen in Figure 3.56 do not appear in the PES spectrum. These modes may be
the vibration modes of the suspension in the vertical direction.
Figure 3.56: Linear spectrum of disk flutter (1 Vrms = 0.11 µm).
Correlation between Disk Flutter and PES
There exist coincidences of the amplitude peaks between the power spectrum
of PES and the power spectrum of disk flutter. Let us now compare the phase
relationship between them. Figure 3.58 shows the time domain signals for the
vertical vibration of disk and the NRRO component of the PES.
It appears that the NRRO component of PES and the vertical vibration
of disk have the same fundamental frequency. We can, therefore, establish a