Use of constraints in the early stages of design

At the very early stages of original design work, the aspects of concept, scheming and analysis tend to merge. It is only as the designer's understanding of the design task increases that these aspects become more substantial and start to separate into distinct activities. The challenge in providing support in the early stages is that the design, and hence its geometry, is necessarily ill-defined. This paper looks at the use of constraint-based techniques as a design aid. Constraints are more clearly identified as they bound what is possible. They allow an initial model of the design to be created from the little that is known. This can be expanded as the design progresses, and, being constraint-based, previously created parts of the model can be refined in the light of subsequent design progress. These ideas are illustrated with an application based on the design of an "erection" system for cartons used for packaging. At the start of the design, all that is known is the form of the carton net. This is modelled to determine the required motion. The constraint model is then expanded to consider the basic folding mechanisms and the requirements for guiding faces.