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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク process capability index ： ウィキペディア英語版 process capability index In process improvement efforts, the process capability index or process capability ratio is a statistical measure of process capability: the ability of a process to produce output within specification limits. The concept of process capability only holds meaning for processes that are in a state of statistical control. Process capability indices measure how much "natural variation" a process experiences relative to its specification limits and allows different processes to be compared with respect to how well an organization controls them. If the upper and lower specification limits of the process are USL and LSL, the target process mean is T, the estimated mean of the process is $\backslash hat$ and the estimated variability of the process (expressed as a standard deviation) is $\backslash hat$, then commonly accepted process capability indices include: _ = } | Estimates process capability for specifications that consist of a lower limit only (for example, strength). Assumes process output is approximately normally distributed. |- | $\backslash hat\_\; =\; \}$ | Estimates process capability for specifications that consist of an upper limit only (for example, concentration). Assumes process output is approximately normally distributed. |- | $\backslash hat\_\; =\; \backslash min\; \backslash Bigg(\},\; \}\; \backslash Bigg)$ | Estimates what the process is capable of producing, considering that the process mean may not be centered between the specification limits. (If the process mean is not centered, $\backslash hat\_p$ overestimates process capability.) if the process mean falls outside of the specification limits. Assumes process output is approximately normally distributed. |- | $\backslash hat\_\; =\; \backslash frac\; \}$ | Estimates process capability around a target, T. $\backslash hat\_$ is always greater than zero. Assumes process output is approximately normally distributed. $\backslash hat\_$ is also known as the Taguchi capability index. |- | $\backslash hat\_\; =\; \backslash frac\; \}\; \}$ | Estimates process capability around a target, T, and accounts for an off-center process mean. Assumes process output is approximately normally distributed. |} $\backslash hat$ is estimated using the sample standard deviation. ==Recommended values== Process capability indices are constructed to express more desirable capability with increasingly higher values. Values near or below zero indicate processes operating off target ($\backslash hat$ far from T) or with high variation. Fixing values for minimum "acceptable" process capability targets is a matter of personal opinion, and what consensus exists varies by industry, facility, and the process under consideration. For example, in the automotive industry, the Automotive Industry Action Group sets forth guidelines in the Production Part Approval Process, 4th edition for recommended Cpk minimum values for critical-to-quality process characteristics. However, these criteria are debatable and several processes may not be evaluated for capability just because they have not properly been assessed. Since the process capability is a function of the specification, the Process Capability Index is only as good as the specification. For instance, if the specification came from an engineering guideline without considering the function and criticality of the part, a discussion around process capability is useless, and would have more benefits if focused on what are the real risks of having a part borderline out of specification. The loss function of Taguchi better illustrates this concept. At least one academic expert recommends the following: However where a process produces a characteristic with a capability index greater than 2.5, the unnecessary precision may be expensive. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「process capability index」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.