Use of axiomatic design principles for analysing the complexity of human–machine systems

Coupling between user goals and user actions has an adverse effect on usability, because it increases the gulf of execution. Based on the principles of axiomatic design, a methodology was developed for identifying and suggesting avenues for eliminating such couplings. A model of a human–machine system is constructed using the following design domains: goal; functional; physical; and action. The mappings between these domains are represented using design equations, which provide a qualitative metric for characterizing the degree of coupling. The use of this methodology is illustrated using several examples, which show that coupling may exist between the goal and functional domains, the functional and physical domains or the physical and action domains. Different loci of coupling have different implications for design improvement. By providing a general and rational criterion, this formalized and analytical methodology has the potential to be a useful tool for design engineers during the early stages of design.