Showing papers by "Daniel D. Frey published in 2017"

A model-based approach to associate complexity and robustness in engineering systems

Abstract: Ever increasing functionality and complexity of products and systems challenge development companies in achieving high and consistent quality. A model-based approach is used to investigate the relationship between system complexity and system robustness. The measure for complexity is based on the degree of functional coupling and the level of contradiction in the couplings. Whilst Suh’s independence axiom states that functional independence (uncoupled designs) produces more robust designs, this study proves this not to be the case for max-/min-is-best requirements, and only to be true in the general sense for nominal-is-best requirements. In specific cases, the independence axiom has exceptions as illustrated with a machining example, showing how a coupled solution is more robust than its uncoupled counterpart. This study also shows with statistical significance, that for max- and min-is-best requirements, the robustness is most affected by the level of contradiction between coupled functional requirements (p = 1.4e−36). In practice, the results imply that if the main influencing factors for each function in a system are known in the concept phase, an evaluation of the contradiction level can be used to evaluate concept robustness.

Design of a cellular-enabled data-logging system for wheelchair use characterization

Abstract: Adoption rates and performance metrics of wheelchairs in low-resource settings are thought to vary significantly based on the type of wheelchair distributed and after-sales services provided. Several organizations have been innovating on low-cost wheelchairs, developing ruggedized designs to better withstand off-road usage. The benefits provided by these wheelchairs, however, have been difficult to measure using traditional approaches and there is a lack of data on the actual conditions these wheelchairs are subjected to in use. In this paper, we present the design of a frame-based and a wheel-based cellular-enabled data-logging system and the associated sensor sampling algorithms to characterize the usage and performance of wheelchairs. The system measures forces and loading on the wheelchair, differentiates between rider self-propulsion or attendant-propulsion, and characterizes wheelchair usage bouts by length, speed, and incline. Using this system, we can collect data on prolonged usage from users in remote regions over a period of 2–4 weeks to understand and differentiate the impact from various improved wheelchair models.