Introduction - Hard Disk Drive: Mechatronics and Control - page 1

Chapter 1
Introduction
The hard disk drive or HDD plays an important role in the modern era of digital
technology. The HDD industry began its journey in 1956, and since then, it
has traveled through a history of extra-ordinary achievements which is rivaled
only by the semiconductor revolution. Storage capacity of the HDD has grown
from mere 5 MB (Mega Bytes) in 1956 on fi fty 24-inch disks to more than 100
GB (Giga Bytes) stored on one disk of 3 2 inch diameter. During this relatively
short period, the HDD industry has fostered excellent innovations in various
scienti fi c and technological disciplines related to the design and manufacturing
of HDD. Mechatronics and control played a vital role in this path of achieving
rapid growth in the capacity of HDD and continuously decreasing cost.
The term Mechatronics, originated in Japan in late 1970s, describes a
branch of engineering that is fi rmly established now. According to the Mecha-
tronics Forum (UK), Mechatronics is the synergistic integration of mechanical
engineering with electronics and control in the design and manufacturing of
product process [138]. A mechatronic system is neither just a marriage of
electrical and mechanical systems nor just a control system; it is a complete
integration of all of them. Everyday we fi nd systems and devices that involve
mechatronics, e.g., a camera with auto-focus and auto-exposure, an automatic
cash machine, a printer, a robot, and an automatic production line etc.
Many mechatronic systems demand for ultra-high precision in controlling
the output of the system. The HDD is one such system where the tolerance
limit for position error is only few nanometers. The HDD includes several
subsystems some of which are mechatronic systems, and the integration of
all these subsystems to realize a practical product is a challenging task. The
mechatronic parts of HDD include the servomechanism that controls the po-
sition of the read-write heads of the HDD and the spindle motor system that
spins the disks at precisely regulated speed. The challenging task of the HDD
servo engineers can be visualized using the following analogy, which helps one
to comprehend the difficulties faced in making an HDD and thus to appreciate
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