GEOMETRIC REASONING IN SUPPORT OF ASSEMBLY-ORIENTED CAD
S J Tate, G E M Jared
SIMS, Cranfield University, Cranfield, Bedfordshire, MK43 OAL, UK.
K G Swift
Department of Engineering, University of Hull, Hull, East Yorkshire, HU6 7RX, UK.
Assembly-oriented CAD has long been accepted as a necessary development
from the current component-focused solid modelling systems. It is proposed
that such an environment should incorporate assembly sequence generation
and Design for Assembly (DFA) analyses to assist the designer, including
some automatic inference to facilitate ease of use. The key to enabling
the various assembly analyses lies in interrogation of the CAD model and
this poses some interesting challenges in the field of geometric reasoning.
Statistics from case studies show that, in particular, the identification
of part symmetry and principal axes is fundamental to many of the required
algorithms which have been identified. This paper reviews methods
for symmetry detection. However, no pre-existing method suitable
for this application is found and so a new technique is proposed which
exploits the existence of loops within the CAD model. This entails
the comparison of loop areas to discover exact symmetry, partial symmetry
and repeated features. Implementation of this technique is described
and in conclusion the benefits and problems associated with it are discussed.