Page 30 - Handbook of Biomechatronics

Introduction 23

within the skeleton of a conceptual model should not be considered as any-
thing more than an idealistic approach to structure the thoughts. Having
taken the disciplinary constraints away from the designer, the methodology
must substitute some form of a safety net. The concept of causality as it was
described through the definition of mathematical isomorphism, presents an
ideal safety net for the system synthesizer to ensure inclusion of fundamental
physical laws. The ideal and conceptual system model is therefore unable to
contravene fundamental disciplinary laws.
The substitution of bond graph multiports for elements of word graph is
the next stage in advancing toward a detailed final design. A simple substi-
tution may, however, prove insufficient in the formulation of a valid bond
graph model, since individual elements of a word graph can quite often rep-
resent rather complex systems. A reasonable multiport may thus greatly
expand the initial model structure. Expansion within the sphere of concep-
tuality must be limited to the introduction of absolutely essential details
ensuring that the bond graph will undergo a minimum reticulation process
through multiport substitution. Inclusion of necessary multiports with their
associated bonds will change the system description from simple word graph
to a more detailed symbolic structure. For the development of the new sys-
tem to be coherent, ideal junction structures that are fundamental to asser-
tion of causality are introduced. The properties of bond graphs, particularly,
the necessity for correct causal structure, quite often dictate alterations to
perceived ideal structure. Such dictated changes are valuable in establishing
the functionality and reliability at earliest stage of a product life cycle. Here,
the possible existence of causal conflicts could direct attention toward unac-
counted factors. Additional elements to cater for insufficiencies can contrib-
ute to further expansions. This process of presenting an idea through causal
word graphs is iterative in the progression of an ICD. Fig. 6 is a diagram-
matical presentation of such a recursive reticulation process.

12.4 Design Criterion

For the reticulation process to sustain an effective progress, the ICD must
satisfy an objective beyond what is imposed by specific disciplinary objective
functions. The functional connectedness which might have been arrived at
through conventional design procedures may not hold any longer. The
biomechatronic problem in its initial proposed format could have more than
a single solution. As a result, some form of criterion that could be applicable
to a great majority of engineering systems is needed to assess alternative