J. Mech. Des. 137(5), 051101 (May 01, 2015); doi: 10.1115/1.4029519
In reconciling the two methods, the paper demonstrates that functions are best used to describe the intended behaviors of large or complex systems, and that function-based design methods can be used to decompose these systems until direct solution is feasible. Affordances are best used to describe what users must be able to do with the functional systems, and show how these descriptions can be organized using action-theoretic models of goal achievement.
The overlap between information used to specify artifact functions and information used to specify affordances occurs at the input/output boundaries of the subsystems found in function-based design methods. In the figure, we can see that the overall state descriptions (shown in red), which enable affordance descriptions (yellow). These affordance descriptions are then mapped with the function-based device descriptions (green) at the input/output boundaries. The paper details an automotive design scenario that begins with the user-centric goal of the vehicle (getting to work) and links this goal all the way down to the design specs (accelerator design).
Due to its focus on the end user, affordance-based design provides powerful tools for the early stages of the design process, including concepts and language for requirement generation in terms of goal achievement and user interaction with the objects and features of their environment. Since affordance-based design lacks dedicated tools for concept generation or the design of product architectures, we identified a way to transition to a function-based approach after this initial stage. This process of applying affordances to high-level, intentional concerns before using functions to address the design of lower-level device behaviors can be applied to any stage of the product’s life-cycle by treating other environmental objects and features such as artifact components, tooling, and machinery in the same manner as the artifact itself.
Red: state descriptions. Yellow: affordance descriptions. Green: device descriptions.