Basic design cycle

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How do you think when designing?

In section 1.1 we saw that the kernel of designing is reasoning from functions to form (geometrical form and physico-chemical form) and use of a new product. It is not possible to deduce the form and the use of a product from its function(s) and in principle many different for a particular function can exist. Therefore in essence design a trial-and-error process that consists of a sequence of empirical cycles. In each cycle by experience, intuition and creativity provisional solutions are generated, which are to be tested for their qualities by theoretical simulations and practical experiments.

In this trial-and-error process the knowledge of the problem and of the solution(s) increases spirally. Roozenburg and Eekels have called their model of this cycle ‘the basic design cycle’ (see figure 1). They claim that the basic design cycle is the most fundamental model of designing, because this cycle can be found in all phases of the design process and is applicable to all design problems, whatever their nature! Someone who claims to have solved a design problem has gone through this cycle at least once.

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Analysis

Figure 1: The basic design cycle (Roozenburg and Eekels, 1995)

Point of departure in product design is the function of the new product, i.e. the intended behaviour in the widest sense of the word. We do not only include the technical function, but also the psychological, social, economic and cultural functions that a product should fulfil. The function need not be laid down in all detail - this is even impossible -, but broad statements on the function must have been made, otherwise the designer does not know what has to be designed.

In section 1.2 we saw that product design is preceded by a product planning phase, which should yield one or more product ideas with, among other things, statements on the functions to be fulfilled. In the analysis phase the designer forms an idea of the problems around such a new product idea (the problem statement) and formulates the criteria that the solution should meet, first broadly and in later iterations more accurately and complete. The list of criteria is called the ‘performance specification’ or ‘program of requirements’. Like the design itself a performance specification cannot be ‘deduced’ from the problem. It is part of the perception that the client, the designer and other ‘stakeholders’ have of a certain problem. A specification comprises all sorts of decisions as to the direction in which solutions will be sought; writing a specification is therefore already a genuine design activity. One can, therefore, arrive at different, equally good specifications for one and the same problem.

Synthesis

The second step in the basic design cycle is the generation of a provisional design proposal. The word ‘synthesis’ means: the combining of separate things, ideas, etc., into a complete whole. Synthesis is the least tangible of all phases of the cycle, because human creativity plays the most important part. But the origination of ideas, seen as a psychological process, cannot be localised in a particular phase of the basic design cycle. The synthesis step is the moment of externalisation and description of an idea, in whatever form (verbally, sketch, drawing, model, etc.) The result of the synthesis phase is called a provisional design; it is not yet more than a possibility, the value of which can only become apparent in the later phases of the cycle.

Simulation

Simulation is a deductive sub process. Simulation is: forming an image of the behaviour and properties of the designed product by reasoning and/or testing models, preceding the actual manufacturing and use of the product. Here, the whole array of technological and behavioural scientific theories, formulas, tables and experimental research methods is available to the designer. Yet, in practice many simulations are based merely on generalisations from experience. Simulation leads to ‘expectations’ about the actual properties of the new product, in the form of conditional predictions.

Evaluation

Evaluation is establishing the ‘value’ or ‘quality’ of the provisional design. To do so, the expected properties are compared with the desired properties in the design specification. As there will always be differences between the two, it will have to be judged whether those differences are acceptable or not. Making such a value judgment is difficult, for usually many properties are involved. Often a design proposal excels in part of these properties, while it is weak in others.

Decision

Figure 2: The iterative structure of the design process (Roozenburg and Eekels, 1995)

Then follows the decision: continue (elaborate the design proposal) or try again (generate a better design proposal). Usually the first provisional design will not be bull’s eye and the designer will have to return to the synthesis step, to do better in a second, third or tenth iteration. But you can also go back to the formulation of the problem and the list of requirements. Exploring solutions appears to be a forceful aid to gain insight into the true nature of a problem: you might therefore often want to adjust, expand, or perhaps sharpen up the initial formulation of the problem. The design and the design specification are thus further developed in successive cycles and in a strong interaction, until they fit one another.

This iterative, spiral-like development of the design and the performance specification has been reflected in figure 2. The design process comprises a sequence of intuitive (reductive) steps and discursive (deductive) steps. Between the two, there is always a comparison of the results attained so far and the desired results. The experience gained in the cycle is fed back, both to the design proposal and to the formulation of the problem and the list of requirements.

References and Further Reading

  • Roozenburg, N. and Eekels, J. (1995) Product Design: Fundamentals and Methods, Chichester: Wiley, 1995, pp. 84-93.
  • Roozenburg, N. and Eekels, J. (1998, 2nd ed.) Productontwerpen: Structuur en Methoden, Utrecht: Lemma, pp. 96-104.
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