Identifying Poor Designs with Conflicts in Design Parameters

Mechanical design is an act of defining machines that produce values to people, however, a poor design sometimes causes mechanisms to fail. Such failures can lead to harms to people, the environment, or both and in the worst case, it can even cause people’s death. Axiomatic design is a design tool that helps the designer come up with more stable and robust designs by pointing out troubling elements in a design by identifying interference among parts. Taking a design through axiomatic analysis only at an abstract level, however, can miss finding interferences within. A product, through its lifetime, can also experience disturbances that the designer overlooked at the time of design. This paper discusses a trouble that arose with bicycles with a new safety feature of locking the front wheel when parked. The locking mechanism faced an unexpected part failure that caused the handle to lock while riding. Another topic is an inherent interference that existed from the very beginning of a design that the designers could not identify probably due to the extreme complexity of the system, the Fukushima Nuclear Power Plant-1, Unit-1. Analysis for evaluating how well a design will meet its functional requirement without trouble should go into the detail level, especially for all modes of operation, to avoid oversight of hard-to-find interferences and conflicts. This paper also suggests carrying out design analysis after production if phenomena, unexpected or unforeseen at the time of design, arise after a product is placed into service.