Hardware Reference
In-Depth Information
the case where the position of the arm is sensed from the side of the actuator.
Similar to the scheme with mechanical push-pin, any vibration due to the
spindle motor and disk rotation, arm and suspension excited by the disk and
air rotation are still present.
Using the grating on the actuator arm solves the problem with heavy mass
of the external mechanical positioner. This, however, does not solve the prob-
lem of keeping opennings in the HDA enclosure. Although there is no need for
a physical contact between the external positioner and the internal actuator,
it still requires a clock head to be inserted for creating tangential reference.
One possible solution is to apply such grating on the spindle motor. With two
gratings, one on the actuator arm and one on the spindle, there is no need
for inserting an external push-pin or external clock head inside the HDA's
enclosure, and the process of STW can be performed outside clean room envi-
ronment. This will reduce the cost of STW process signi
fi
cantly, provided the
gratings are available at cheap price. Current cost of these diffraction grat-
ings makes this approach not suitable for commercial application. It should
be noted that each HDD is required to be provided with a pair of diffraction
gratings only for the sake of STW process and these gratings are never used
in the life of the HDD.
5.3 Media STW
Two methods described earlier, the conventional method with mechanical
push-pin and with optical push-pin, writes the servo patterns on the disks
using the write heads of the HDD. These methods, also known as HDA servo-
writing, are carried out after the components have been assembled inside the
HDD enclosure. The Media STW , on the other hand, creates the servo pattern
on the disks prior to the assembly of the HDD. High precision, high rotating
speed spindle motor and low vibration mechanics are used for writing mul-
tiple disks simultaneously at higher accuracy. Such servo writers which are
independent of HDA and writes servo at recording media level were devel-
oped [155] [150] [191]. These equipments are known by different names such as
multidisk servo track writer , media level servo track writer (MSTW), or bulk
servo writer .
The servo writing process consists of two stages. The
fi
rst stage writes the
servopatternsonasmanyastendisksormoresimultaneouslyinacleanroom
using the MSTW machine. These servo written disks are later assembled
in the HDD. If each HDD contains only two disks, an MSTW writing 10
disks simultaneously effectively writes servo patterns for
fi
ve HDDs in one run.
Writing multiple disks at a higher spindle speed means shorter writing time
per disk leading to better throughput of the servo writing process. The MSTW
uses active air bearing spindle motor with very low vibration, low vibration
actuator mechanism, and high speed electronics which can not be used in
