Specifications

10 Design Case Studies
10-20
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-disk read/write head
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 damping
coefficient of the bearings, is the return spring constant, is the motor
torque constant, is the angular position of the head, and is the input
current.
Taking the Laplace transform, the transfer function from to is
Using the values kg , Nm/(rad/sec), Nm/rad,
and Nm/rad, form the transfer function description of this system.
At the MATLAB prompt, type
J = .01; C = 0.004; K = 10; Ki = .05;
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=
JC
KK
i
θ
i
i
θ
Hs
()
K
i
Js
2
Cs K++
----------------------------------
=
J 0.01= m
2
C 0.004= K 10=
K
i
0.05=