標題: Capability adjustment or gamma processes with mean shift consideration in implementing Six Sigma program
作者: Hsu, Ya-Chen
Pearn, W. L.
Wu, Pei-Ching
工業工程與管理學系
Department of Industrial Engineering and Management
關鍵字: quality management;dynamic C(pk);gamma distribution;mean shift;process capability index
公開日期: 1-十二月-2008
摘要: In the 1980s, Motorola, Inc. introduced its Six Sigma quality program to the world. Some quality practitioners questioned why the Six Sigma advocates claim it is necessary to add a 1.5 sigma shift to the process mean when estimating process capability. Bothe [Bothe, D.R., 2002. Statistical reason for the 1.5 sigma shift. Quality Engineering 14 (3), 479-487] provided a statistical reason for considering such a shift in the process mean for normal processes. In this paper, we consider gamma processes which cover a wide class of applications. For fixed sample size n, the detection power of the control chart can be computed. For small process mean shifts, it is beyond the control chart detection power, which results in overestimating process capability. To resolve the problem, we first examine Bothe's approach and find the detection power is less than 0.5 when data comes from gamma distribution, showing that Bothe's adjustments are inadequate when we have gamma processes. We then calculate adjustments under various sample sizes n and gamma parameter N, with power fixed to 0.5. At the end, we adjust the formula of process capability to accommodate those shifts which can not be detected. Consequently, our adjustments provide much more accurate capability calculation for gamma processes. For illustration purpose, an application example is presented. (C) 2007 Elsevier B. V. All rights reserved.
URI: http://dx.doi.org/10.1016/j.ejor.2007.07.023
http://hdl.handle.net/11536/8099
ISSN: 0377-2217
DOI: 10.1016/j.ejor.2007.07.023
期刊: EUROPEAN JOURNAL OF OPERATIONAL RESEARCH
Volume: 191
Issue: 2
起始頁: 516
結束頁: 528
顯示於類別:期刊論文


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