偏態校正方法之目標平均數管制圖的設計

The Design of Goal Average Control Chart through a Skewness Correction

近年來，製程能力指標〈process capability index〉與管制圖為統計製程管制的重要工具之一，對於品質及生產力之改善有非常良好的效果。本研究利用製程能力指標結合損失函數與偏態校正（skewness correction）方法建構目標平均數管制圖，本研究所提出的管制圖較傳統管制圖更適合使用在偏態的製程上面；再者，因為採取偏態校正的方法決定管制界限，因此本研究所提出的管制圖會有較低的型一錯誤〈type I error〉機率，並且也提供品質改善的目標建議。本研究以汽車風箱上蓋為例，透過本研究所提出的方法評估產品製程，其結果顯示本研究的方法可協助企業改善產品品質、降低品質成本和提升市場競爭優勢。

關鍵字: 製程能力指標、品質損失函數、偏態校正、管制圖。

Process capability index and control chart are important tools in the statistical quality control and they have a good effectiveness on monitoring and improving a process. The study considers the process capability index, quality loss function and skewness correction method to conduct a goal control chart. The proposed control chart is more suitable to be used to monitor a non-normal process than a traditional control chart. Moreover, the proposed control chart has low type I error probabilities on monitoring a non-normal process since it employs skewness correction method to determine control limits and provides a goal suggestion of quality improvement. This study also considers the proposed goal control chart using the top of a motor evaporator. In the example, the goal standard deviation and control limits can help practitioners in making production decisions and improving a process.

KEYWORDS:process capability index, quality loss function, skewness correction, control chart.