CASE STUDY
ANSYS and Dell Xeon Keep Hutchinson On Top
In Disk-Drive Business
HUTCHINSON TECHNOLOGY, INC.
Introduction
Hutchinson Technology, Inc. (HTI), manufacturer of a
crucial component in computer disk drives – the
suspension assembly – is running hard to stay in place.
Its “place,” however, is on top: it is the No. 1 supplier
of suspension assemblies to disk drive manufacturers.
EXECUTIVE SUMMARY
Challenge:
To meet design and development needs
HTI’s hard-running shows up most clearly in engineering and Design for Manufacturability (DFM). In
design, engineers strive for the highest performance in
the existing array of products. At the same time, they
are developing new products before customers ask for
them. This minimizes pre-production lead-times and
helps customers keep pace, or ahead of, disk drive
technology.
of manufacturing suspension
assemblies for computer disk drives.
Solution:
Implement ANSYS Mechanical and
ANSYS Structural software to the
design of suspension assemblies for the
hard-disk industry.
Benefits:
Use
the ANSYS analysis to show
HTI customers the many trade-offs
needed to balance each design’s
physical properties.
Enables HTI to stay ahead of
customer needs and ahead of the
demands of the disk-drive industry
for greater speed and smaller, more
precisely engineered components.
Allows
HTI to determine frequencies
Shown is the suspension assembly for a computer
hard-disk drive.
A vital part of HTI’s new product work is design
verification and optimization with finite element
modeling and finite element analysis (FEM/FEA). In a
hard disk drive, suspension arms actuate back-andforth across spinning disks, constantly accelerating
and decelerating between data tracks that are only 125
nanometers wide (5 micro inches) and packed in at
120,000 tracks per inch. As such, the arms must combine rigidity and flexibility with low inertia and fast
damping of the most minute off track motion.
by using ANSYS modal analysis.
In their DFM efforts, engineers focus on tooling to
speed up and simplify manufacturing, always with the
goal of minimizing variability and lowering cost. The
automated processes for suspension assemblies are
finely tuned and will not accommodate even the
tiniest amount of part-to-part or batch-tobatch variability.
To meet both design and development needs, HTI
relies on ANSYS Structural and ANSYS Mechanical
software.
Challenge
For HTI, the biggest business challenge is the disk
drive technology itself. Over the past 10 years, data
storage capacity has grown by a factor of 10,000. In
recent years, data densities have soared in terms of
bits per square inch. Manufacturers have reduced the
number of disks per drive assembly to one or two
instead of four or more a few years ago. As a result,
the average number of suspension assemblies per
disk drive has fallen from 4.5 in 1999 to 2.4 in 2002.
HTI’s parts are tiny—three to five components in an
assembly little more than an inch long. They are
etched, stamped and laser welded at one-a-second
rates on specially built machinery. Physical properties
are critical and much of this lies in the painstaking
way the parts are formed and joined. For example,
arms have an embossment around the hinge opening
that requires up to 14 individual forming operations.
A suspension assembly lies above or below every disk
in a disk drive. If there are multiple disks, there are
two suspension assemblies between each pair of
disks. Tiny read/write heads—barely a millimeter
long—are mounted at the small end and fly on air
pressure at about 10 nm or one-millionth of an inch
above that of the disk’s spinning surface. (A human
hair is about 40,000 nm thick.) Holding the suspension assembly in place vertically is a force of two
grams with a tolerance of plus or minus 0.1 gram.
Outputs include static, modal, and
harmonic frequencies and the
frequency gain, a logarithmic
function of the assemblies unwanted
mechanical displacement.
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“Designing ahead of the market allows us the processing and tooling lead
times that we need.”
—Mark Miller, HTI Principal Engineer
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“ANSYS helps us with competitiveness by identifying long-lead time items and
indicating factors that might lower manufacturing yields. ANSYS also helps us
CASE STUDY
avoid the time and cost of having to make physical prototypes.”
“One of the most important design criteria is the
control and damping of the suspension assembly
and heads motion as it stops to read a track,”
explains Ray Wolter, HTI development engineering supervisor. “The motion or mode shapes we
look at are expressed in terms of frequency.
Magnitude of the motion—the distance away from
the track to be read—is dependent on the rates of
acceleration and deceleration of the arm. These are
a major factor in the disk drive assemblies overall
speed of data retrieval.”
The need for big RAM in analysis was explained by
Yiduo (“Eddie”) Zhang, P.E., senior product design
engineer. “Most of our stress analysis are relatively
simple linear models but we have to use lots of
elements” to ensure the accuracy of the model and
the precision in the results. There is no room for
error. “We used 300,000 brick elements in one stress
analysis,” he observed. “That meant about one
million degrees of freedom (DOFs) had to be
handled in the analysis.”
Wolter and his team were pleased with ANSYS performance on the Dell machines. The main reason for
the speed-up—which has not yet been quantified—
is that the Dell 32-bit computing architecture running Windows XP allows the use of RAM up to the
maximum for ANSYS.
Zhang added that speed is especially important “in
repetitive analysis which we do all the time, things
like rerunning a linear analysis after just changing
load conditions and constraints. We do hundreds of
these with the ANSYS sparse solver. They now run
10 times faster, from two minutes per load step to
less than 12 seconds,” he said.
Solution
The fundamental design challenge for HTI always
comes back to the frequency of vibration for the suspension assembly. “We have to make sure the suspensions’ natural frequencies are sufficiently far
away from those of the full disk drive assembly that
they won’t resonate with and amplify each
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mass-lifting efficiency, and the vertical spring rate
of the arm, plus shock (mass times inertia)
measured as a multiple of the force of gravity.
All these factors ultimately show up in the
read/write-heads minute “gimballing” movement at
the tip of the suspension assembly.
Ray Wolter, development engineering supervisor at
Hutchinson Technology Inc., Hutchinson, Minnesota,
with two disk drives, showing the effects of Moore’s
Law and storage device gains.
other,” Wolter said. “If the frequencies resonate with
high amplitude, the arm will take longer to settle
over its track. We have to tie all our design changes
back to those frequencies.”
“The available frequencies outline the design envelope and we use ANSYS to calculate those frequencies,” Bjorstrom explained. “Often we do one DOE
analysis for stiffness and another for flexure mass
spring rate and shock. We may do as many as 20 to
30 iterations each of multiple analysis. We get
output in a big matrix and speed is critical.”
To raise an arm’s frequency or steer clear of drive
natural frequencies, “we can shorten the part or
make it wider or thicker or a combination of those,”
Wolter noted. “ANSYS helps us look at that. The
DOE approach manages the inputs across the
number of ANSYS runs needed to generate
frequencies of parameter changes, both individually
and in combination. ANSYS will output all the frequencies, stiffness and loads,” he explained. “We
graph those outputs and let the curves and crossover
points show us the optimum design parameters.”
Benefits
Wolters’ team of design engineers uses ANSYS to
show customers the many tradeoffs needed to
balance each design’s physical properties.
These include bend, torsion, sway, flexibility for
dealing with shock, the suspension assemblies
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275 Technology Drive
Canonsburg, PA 15317
U.S.A.
[email protected]
ANSYS is also a key HTI tool in staying ahead of
its customers’ needs. “Designing ahead of the market allows us the processing and tooling lead times
that we need,” said Mark Miller, an HTI principal
engineer. “It helps us with competitiveness by
identifying long-lead time items and indicating factors that might lower manufacturing yields. ANSYS
also helps us avoid the time and cost of having to
make physical prototypes.”
The other FEA advantage, Miller continued, is
“building a knowledge base in case a customer
wants to drill down into the details of the analysis
such as design alternatives and data on trade-offs.
Customers often do that, too, as their designs
evolve,” he added, “or if they need to take
advantage of new technology opportunities or to
meet competition.”
Determining frequencies is done with ANSYS and
modal analysis, which also reveals the mode
shapes. “Outputs include static, modal and harmonic frequencies and the frequency gain, a logarithmic
function of the assembly’s unwanted mechanical
displacement,” said Miller. Tight control of gain
leads to less off track motion, which leads to more
tracks on the disk, which leads to higher “areal”
density (the amount of data that can be stored in a
given unit of area on a disk).
In sum, rapid advances in computer hardware combined with a true 32-bit operating system allow HTI
to build and speedily solve huge FEA models. This
lets the design engineering team stay ahead of
customer needs – and ahead of the ceaseless
demands of the disk drive industry for greater speed
and smaller, more precisely engineered
components. HTI’s shrewd use of these technologies helps ensure that it will keep its
commanding lead.
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