Article published VIRTUAL REALITY
Collision detection gets more realistic
The collision detection engine developed by the CEA/List determines the minimal distance between parts with complex forms, and does so in real time. It also enables designers to perform interactive mechanical simulations in a realistic way. LMD++ is now available and integrated into Catia.
In the world of industrial design,
detecting collisions is important to
determining whether parts can be
assembled (or disassembled) given
their bulk, the space available,
and possible trajectories. CAD
and virtual reality can check this
without a physical model, but with
considerable limitations:
«Most collision detection engines
take one instant in the assembly
phase and use geometric computing
to check that there is no overlap
between the parts, which never
happens in reality», explains Xavier
Merlhiot of CEA/List. «In other words,
these engines determine after-thefact
that a simulated situation was
impossible.»
CEA/List's goal was to enhance
realism, leading to two key choices:
interactive real-time software (the
designer simulates assembly of
the part with a haptic interface and
determines him/herself whether
the assembly is collision-free) and
especially, computation centred
on possible situations (positive or
even zero local minimum distance
b e t we e n p ar t s) rat h e r t h an
impossibility determined after the
fact (penetrations).
The LMD++ engine does not use
mathematic formulas for continuous
description of the parts; rather,
it represents them discreetly as
hundreds of thousands of triangles,
with perfect control over the level
of geometric approximation. The
designer can also set up a more dense
mesh (millions of triangles) for very
precise distance calculations, if real
time isn't necessary.
Developed initially for Renault, PSA,
and Dassault Aviation, the tool has
proven formidably realistic. The
real-time feature enables checking
the feasibility of an assembly (or
testing various scenarios) all while
calculating exactly how much
time the operation will take. The dimensions of a part can be «blown
up» by simply changing the settings
to accommodate dimensional
tolerances for production.
The computer scientists at CEA/List
made an effort to facilitate the
designer's task. Without any manual
processing, the scenario elements
can be managed according to their
topology, using volume models
(foundry parts), surface models
(sheet metal), or linear models
(cables).
What's even more significant, LMD++
can perform simulations on parts
for which the CAD model has defects
(housing not sealed, for example),
without forcing the designer to
make tedious and often premature
corrections. The defects are of course
indicated, but if the designer decides
they won't impact the simulation,
he or she can proceed to launch the
program.
This robust new tool is designed
for daily use. It is coupled with a
movement solver (developed by CEA/
List to calculate the contact loads)
and already integrated as a plug-in
for Catia V5, marketed by start-up
Haption. The current product is for
rigid parts, but by the end of 2007,
a new version will also be able to
handle deformable parts.
