Hardware Reference
In-Depth Information
by an analysis on the correlation between the disk flutter and TMR.
Measurement of Disk Flutter
Figure 3.53 shows an experimental setup for measuring the vertical vibration
of the disks. A 3.5” glass disk of 1.27 mm thickness is spun at the speed
of 4800 RPM by a fluid dynamic bearing (FDB) spindle motor. The system
uses the micro positioner
‡
PA-2000 to position a slider with 0.42 µmwide
write head, which is used to perform servo track writing. A clock head is
also available to provide the necessary timing signal during the servo writing
process. Approximately 0.3 µm wide servo tracks are created by erasing part
of the servo bursts. The read sensor has a width of about 0.25 µm. A Laser
Doppler Vibrometer (LDV
§
) is used to measure the slider's vertical vibration
by shining a spot on the slider with a perpendicular laser beam. The LDV
measures the velocity of the slider and derives the displacement from there. A
position error signal (PES) processing channel is also used [61] to measure the
displacement of the slider parallel to the disk surface.
Figure 3.53: Experimental setup.
The model of the actuator is identified by injecting a swept sine signal into
the voice coil motor (VCM) and measuring the frequency response using a
Hewlett Packard dynamic signal analyzer (DSA) 35670A. The model of the
‡
MicroE Systems Inc.
§
Polytec GmbH, model OFV512.
