Robust Product Design Optimization Method Using Hierarchical Representations of Characteristics

Product design optimizations usually require the optimization of not only all performance characteristics, but also the robustness of certain performance characteristics. Obtaining optimum design solutions is far from easy, since this requires evaluations of numerous related characteristics that usually have complicated and conflicting interrelationships. Some of these characteristics can include variations of one type or another, such as manufacturing process variations, variations pertaining to the environments where the product is used, variations in how long-term use affects certain product characteristics, and so on. The difficulty of obtaining optimum design solutions is thus compounded by the need to carry out specific optimizations that provide sufficient robustness to safely accommodate anticipated ranges of variations. This paper expands the hierarchical multiobjective optimization method based on simplification and decomposition of characteristics so that optimizations can be concurrently conducted for both performance characteristics and maximization of robustness against characteristic variances. A principal cause of variations in performance characteristics is variations in the contact conditions of joints, and the utility of the proposed robust product design optimization method is demonstrated by applying it to machine-tool models that include joints.

A Coordination-Based Approach to Robust Product Design

Robust product design is a two-objective optimization problem in nature. On the one hand, it is wished to minimize variations in product performance (i.e. first goal); on the other hand, it is desired to maximize product functionality (i.e. second goal). As known, these design goals may not arrive at their own optima at the same time; therefore, coordination between the two perfonning goals is needed during the design iterations to help achieve high robustness in product performance in the sense that a best compromise design is reached. In this work, a coordination-based robust design approach is developed to control the computational aspect of robust design process in a coordinated fashion, allowing that high-quality engineered products are produced with designing-in of performance precision and accuracy through robust design. A fuzzy control algorithm in terms of coordination rules prescribed is generated for handling design coordination by tuning an adaptive design parameter β, defined over the domain from 0 to 1.0. Three coordinated design models are discussed along with the study of a design example.