June
22, 1998 Design News
ENGINEERING NEWS
Reverse engineering takes giant leap
forward
Advanced computer software
and technology make reverse engineering a powerful tool
for just about everything
by Laurie Peach, Associate Editor
Arlington, VA--Dinosaurs. The evolution of
gorillas. An Olympic snowboard helmet. A Navy wildcat
pulley. A machine part.
What do all of these have in common?
Reverse engineering--the process of engineering backward
to build a CAD model, geometrically identical to the
original. For all these projects, engineers took electronic
measurements of points from a structure's surface, and
fed the data into CAD software, which turned the information
into smooth surface models.
While the concept of reverse engineering is not new,
computer and software advances have made it a powerful
tool. The technology is particularly useful for non-planar
or curved surfaces. A complicated machine part can be
copied with digital accuracy. And done quickly.
The U.S. Navy hired Advanced Marine Enterprises, Inc.
(AME), a naval architecture and marine engineering firm,
to make recommendations on how to fix a malfunctioning
wildcat. Advanced Marine engineers had a mere five-day
window to capture the exact physical geometry of the
port and starboard side anchor handling systems from
an active Navy ship. The system included two 5-ft diameter
wildcats, the sprockets that mesh with the anchor chain.
To model the wildcats accurately and quickly, the company
turned to reverse engineering and HighRes Inc. (LaJolla,
CA), a dynamic software company specializing in reverse
engineering software.
Braxton Carter, president of HighRes Inc., developed
the C++-based software with a Cadkey interface from
Baystate Technologies (Marlborough, MA). Although originally
slated for "mom and pop" organizations with
an entry-level price of $2,995, HighRes now handles
several high-profile jobs. In the design halls of Disney,
Carter digitized dinosaur fossils for Disney's newest
theme park, Tomorrowland. In the jungles of Madagascar,
Carter trained a team from the University of Massachusetts
(Amherst) to digitize gorilla skulls to determine the
animal's evolution based on skeletal models. Now, the
U.S. Navy.
The anchor chains on the LSD49 run from chain lockers,
up over deck bolsters, around the powered wildcats with
about 180 degrees of wrap, and finally, down through
another set of bolsters toward the anchors. Each chain
link, made from 3-inch diameter bar stock, 18 inches
in length and weighing 90 lbs, should sit flat in the
pocket of the wildcat whelps (teeth). In this case,
the links of the ship's port side chair sometimes ride
up the face of the whelps rather than sitting in the
pockets, which presents the danger of the anchor falling
uncontrollably.
Wildcats are not manufactured with tolerances that
allow them to be used with any nominal 3-inch chain.
The manufacturer grooms each wildcat to fit a specific
chain sample at the factory by chipping, grinding, air-arc
cutting, and/or building up weld clad. Several groomings
conducted on the port side wildcat over its five-year
life did not eliminate the problem.
Enter HighRes. Equipped with a 3DLX 5-axis coordinate
measuring machine (CMM) and HighRes STUDIO software,
Carter, went to work. "I needed to create a geometric
IGES 128 surface data format," says Carter.
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Baxton Carter, president of HighRes, used
a meshed algorithm technique to reverse engineer
the polygonal wildcats. He taped primary and
secondary lines and followed these with a digitizer.
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Carter only had five days before the ship went out
for missile tests. Originally, he took sliced data
measurements. "I would have ended up with a rigid
model if I continued this way," he says. Instead
he used a series of curves and a meshed algorithm technique.
Carter drew primary and secondary lines around the surface.
"It looked like a tic-tac-toe board," he says.
The unique benefit of HighRes is its ability to move
around free forms. This method provides x, y, and z
coordinates of points on the surface to a tolerance
of 0.012 inch.
To accompany the IGES surface model, a miniature wax
prototype was machined with FastNURBs software on a
Micro CNC mill from Flashcut NC. Machining the miniature
part allowed Carter to verify the surface data by holding
the actual physical part in his hand. Carter says, "Desktop
engineering tools now allow a cost effective integrated
set of tools for part verification."
While Carter digitized, Peter Herrman and Jerry Miller
of AME, and John Coon of the Navy, took manual 3D measurements
using a chalk line plum bob and tape measure. They measured
the hawse pipe deck bolster and chain pipe bolster locations
relative to the wildcats as well as the profile of the
hawse and chain pipe bolster surfaces in the chain contact
area.
Miller used these measurements to create 3D models
in the Intergraph? environment. When combined with
the wildcat models and a parametric model of the chain,
AME engineers could assess fit-up and alignment issues.
Virtual simulation. Brian Bergmann,
section chief at AME, explained: "The CAD model
not only allowed static fit tests to be conducted, but
also was exported to a 3D mechanical system simulation
code, ADAMS?. Since the ride-up problem was originally
aggravated at higher wildcat speeds and chain tensions,
AME proposed a dynamic simulation to gain a better understanding
of the important variables. The plan is to use the model
to build confidence that the recommended alterations
will work prior to cutting steel."
Michael Bizier, AME simulation engineer, selected the
best code and method for modeling the contacts between
the complex surfaces of the chain links, bolsters, and
wildcat. He says, "We imported the geometry of
the components from the CAD model and set everything
up to interact." They modeled surface contact normal
forces as well as static and kinetic friction. The scale
of this contact problem was beyond what AME or the ADAMS
developer Mechanical Dynamics Inc., had addressed before,
says Bizier. "[So] we purchased a Contact Dynamics
Toolkit to supplement the ADAMS code and consulted with
Sam MacDonald, MDI's contact dynamics expert."
Eventually, Bizier was able to apply tensile forces
to represent chain and anchor weight, and then rotate
the wildcat on the computer screen.
Bergmann says the company hopes this technique will
prove successful. "Perhaps down the road, computer
models will replace the current practice of constructing
working physical models of anchor, chain, wildcat, chain
locker, and bolsters, presumably with significant cost
savings."
At the time the author wrote the article, simulation
and final report had not been completed.
Turnaround time from proposal to suggested solutions
will be approximately four months. Mapping of the wildcats
with reverse engineering and HighRes was an essential
part of this task. "We considered other methods
such as laser scanning and photogrammetry to obtain
surface models, but the mechanical arm digitizing method
was found to be better suited for this application,"
says Bergmann.
He adds that the ultimate goal will be to design and
test modifications on the computer screen rather than
through trial and error with full-size hardware, resulting
in tremendous time and cost savings.
What this means to you:
Reverse engineering of mechanical parts can be useful
when:
-
CAD models are unavailable or unusable for parts
that must be duplicated or modified
-
CAD not used in original design; inadequate documentation
on original design
-
Original CAD model not sufficient to support modification
or manufacturing using modern methods
-
Original supplier unable or unwilling to provide
additional part information
-
Shop floor changes to original design
Lockheed Martin advances JSF, F-2
by Rick DeMeis, Associate Editor
Ft. Worth, TX--Keying on its F-16, Lockheed
Martin is pushing technology in two programs. The effort
to develop the X-35 demonstrators for its Joint Strike
Fighter (JSF) design saw flights by the Calspan (Buffalo,
NY) operated Variable stability In-flight Simulator
Test Aircraft (VISTA). The aircraft computers were reprogrammed
to fly with the same dynamic response as envisioned
for the JSF in order to evaluate and refine flight-control
software. Evaluation maneuvers included simulated aircraft
carrier landing approaches, aerial refueling, air-to-air
combat tracking, and formation flying.
Assembly has also begun at the company's famous Skunk
Works on the first of two X-35 demonstrators. For this,
an "agile tooling" concept is being used to
both assemble and mate aircraft components in the same
tools. The first aircraft reaches final assembly later
this year, to be followed immediately by the second
in the same tools, for airframe commonality.
Lockheed Martin is teamed with Northrop Grumman and
British Aerospace in developing its JSF design in competition
with a Boeing-led group. The first of about 3,000 aircraft
are scheduled to enter service in 2008 for U.S. forces
and the Royal Navy (DN 2/17/97, p. 19).
Elsewhere, Japan's Mitsubishi Heavy Industries has
awarded Lockheed Martin a second major contract to continue
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