Toward Time-Dependent Robustness Metrics

Abstract

Quality characteristics are often treated as constants in robust design, while many of them actually vary over time. It is desirable to define new robustness metrics for time-dependent quality characteristics. This work shows that using the static robustness metrics for time-dependent quality characteristics may lead to erroneous design results. We then propose criteria of new robustness metrics for time-dependent quality characteristics. Instead of using an expected point quality loss over the time period of interest, we use the expectation of the maximal quality loss over the time period to quantify the robustness for time-dependent quality characteristics. Through a four-bar function generator mechanism synthesis, we demonstrate that the new robustness metrics can capture the full information of robustness of a time-dependent quality characteristic over a time interval. The new robustness metrics can then be used as objective functions for time-dependent robust design optimization.