Abstract
A possible goal in robust design of dynamic systems is
to find a system topology under which the sensitivity
of performance to the values of component parameters is
minimised. This can provide robust performance in the
face of environmental change (resistance variation with
temperature, for example) and/or manufacturing-induced
variability in parameter values. In some cases, a
topology that is relatively insensitive to parameter
variation may allow use of less expensive (looser
tolerance) components. Cost of components, in some
instances, also depends on whether 'standard-sized'
components may be used or custom values are required.
This is true whether the components are electrical
components, mechanical fasteners, or hydraulic
fittings. However, using only standardsized or
preferred-value components introduces an additional
design constraint. This chapter uses genetic
programming to develop bond graphs specifying component
topology and parameter values for an example task,
designing a passive analog low pass filter with
fifth-order Bessel characteristics. It explores three
alternative design approaches. The first uses
'standard' GP and evolves designs in which components
can take on arbitrary values (i.e., custom design). The
second approach adds random noise to each parameter and
evaluates each design ten times; then, at the end of
the evolution, for the best design found, it 'snaps'
its parameter values to a small (component specific)
set of standard values. The third approach uses only
the small set of allowable standard values throughout
the evolutionary process, evaluating each design ten
times after addition of noise to each standard
parameter value. Then the best designs emerging from
each of these three procedures are compared for
robustness to parameter variation, evaluating each of
them one hundred times with random perturbations of
their parameters. Results indicated that, for this
preliminary study, the third method produced the most
robust designs, and the second method was better than
the first.
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