Tham khảo tài liệu 'volume 20 - materials selection and design part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The most important element in the successful practice of robust design is the characterization of the performance. As an example consider an electrical resistor. Its performance is usually characterized by the resistance R. However the value of R is not important to quality and reliability. Any nominal value of R that is desired is easily achieved. The characterization R already assumes a linear relationship between voltage and current with R being the slope of the assumed straight-line relationship between voltage and current. The specific value of R is not of primary interest in optimizing the robustness of the resistor. Rather the quality of the straight-line relationship between voltage and current is important. Therefore voltage is plotted versus current with two noise conditions noise values that cause small current and noise values that cause large current. The most robust resistor is the one that has the least deviation from a straight line which is the ideal performance of the resistor. The smallest value of the ratio of the deviation from the straight line divided by the slope of the straight line is needed. After further analysis the square of the ratio is taken. Therefore the ratio of the average of the square of the deviations averaged over all data points is divided by the square of the slope of the best-fit straight line through the data. This is the measure of robustness. Taguchi developed a set of such metrics to which he gave the name signal-to-noise SN ratios. Larger values of any SN ratio represent more robustness. The most important steps in robust design are 1. Define the ideal performance - often not simple to do 2. Select the best SN definition to characterize the deviations from ideal performance 3. Develop the sets of noises that will cause the performance to deviate from the ideal After some experience the use of the design of experiments to rapidly increase the SN value is relatively straightforward. As an example a subsystem is .
