The preliminary ideation phase, determining more than 70 % of a project’s total costs, is a crucial part of the design process. It usually gathers several actors around the innovative solving process of a complex problem : it merges their complementary expertise, the use of mediating objects as well as a mysterious part of creativity in order to reach a solution if not innovative, at least satisfactory.
With the introduction of always more powerful Computer Aided Design tools, industrial design sees its every-day practices drastically evolving : these software still not support designers during their preliminary design phases and free-hand sketches, on the other hand, encounter increasing difficulties to meet today time-to-market pressures.
This thesis analyzes free-hand sketches’ and CAD tools’ respective and complementary strengths as supports to preliminary design phases. Advanced design engineering concepts, nurturing the study of the particular articulation existing between both mediating objects, are associated with dedicated Human Factors methodologies for the analysis of every-day professional practices. The research project draws its main qualitative and quantitative results from three field studies and two experimentations, bringing together more than forty professional designers and three design companies.
Its multi-disciplinary approach leads to models and recommendations that directly nurture the definition of a new design support system. The specifications tend to respect, augment or, on the contrary, reject some aspects of these mediating objects and aim at supporting a design process always in respect with designers’ constraints and real needs.
Beyond the concepts of our support system, we discuss some results that are of interest for communities of design engineering and human-computer interaction. Among these results are :
- the extension of the preliminary design phase’s boarders ;
- the non-dichotomous approach of rough and detailed mediating objects ;
- the coexistence of two design moves : in addition to Schön’s «see-transform-see» theory, the externalization of a strong mental image or a strong pre-inventive form explains the early uses of CAD tools ;
- the study of tool’s uses and misuses and graphic and semantic contents of external representations all along the design process, reintroduced in a simplified four-steps model ;
- the study of shifts occurring between 2D and 3D representations and their implications for the system’s automatization ;
- and, at the strokes’ scale, the study of the exploitable key-features and the strokes’ cycles and their implications for the temporality of assistance.
The thesis also discusses the added-value of its theoretical and methodological background for the materialization of a design-engineering community that articulates designer, mediating objects, design process and end-users in a coherent system, sound basis for the specification of adapted and adopted design support systems.