User`s guide

9 Design Case Studies
9-20
Hard-Disk Read/Write Head Controller
This case study demonstrates the ability to perform classical digital control
design by going through the design of a computer hard-d isk read/write he ad
position controller.
Using Newton’s law, a simple model for the read/write head is the differential
equation
where is the inertia of the head assembly, is the viscous d amping
coefficient of the bearings, i s the return spring constant, is the motor
torque constant, is t he angular position of t he head, and is the input
current.
Taking the Laplace transform, the transfer function f rom to is
Hard Disk Drive
Disk Platen
Disk Drive Motor
Read/Write
Head
Solenoid
Ω
θ
l
J
d
2
θ
dt
2
----------
C
d θ
dt
-------
K θ++ K
i
i=
J
C
K
K
i
θ
i
i
θ
Hs()
K
i
Js
2
Cs K++
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