国标《常规控制图》中的几个问题探析

中华人民共和国国家标准<常规控制图>(编号GB/T 4091-2001)是SPC的权威文件,但也存在一些瑕疵.首先,对计件控制图分布的表述不妥当;其次,判异准则8的设计有一定的随意性;最后,判异准则3的文字叙述与给出的示意图之间有出入.希望有关专家下一次修订<常规控制图>国家标准时能够改正这些问题,维持国标的权威性.     

理解SPC控制图的关键——小概率原理

当前SPC技术已经广泛应用于大批量生产中的工序质量控制.如何从本质上理解控制图的原理及控制图异常情况的判断,成为不少质量管理人员关心的问题.文章通过对SPC控制图中小概率原理的叙述,说明了理解SPC控制图的关键是小概率原理.     

基于可变样本容量的计数值控制图的改进

文章在对计数值控制图的控制限的设计上提出了一种新的方法.计数值控制图--如P图和U图在面对样本容量不同的样本时往往会出现不同样本的控制限不一致的情况,这就需要对控制限的设计进行一定的变型.以往所提出的方法有取均值和标准化等,文章提出的方法是对给定的参数,如不合格品率p值进行变型,加上一个权重值,建立了一个新的控制图,即加权计数值控制图,使之在计算控制限时可以规避不同样本容量所带来的问题.     

Control Charts for the Variance and Coefficient of Variation Based on Their Predictive Distribution

This article develops a control chart for the variance of a normal distribution and, equivalently, the coefficient of variation of a log-normal distribution. A Bayesian approach is used to incorporate parameter uncertainty, and the control limits are obtained from the predictive distribution for the variance. We evaluate this control chart by examining its performance for various values of the process variance.     

On the run length of a Shewhart chart for correlated data

We consider an extension of the classical Shewhart control chart to correlated data which was introduced by Vasilopoulos/Stamboulis (1978). Inequalities for the moments of the run length are given under weak conditions. It is proved analytically that the average run length (ARL) in the in-control state of the correlated process is larger than that in the case of independent variables. The exact ARL is calculated for exchangeable normal variables and autoregressive processes (AR). Moreover, we compare this chart with residual charts. Especially, in the case of an AR(1)—process with positive coefficient, it turns out that the out-of-control ARL of the modified Shewhart chart is smaller than that of the Shewhart chart for the residuals.     

Formulas for the Design of CUSUM Quality Control Charts

ABSTRACT

In the design of CUSUM control charts, it is common to use charts, tables, or software to find an appropriate critical threshold (h). This article provides an approximate formula to calculate the threshold directly from prespecified values of the reference value (k) and the in-control average run length (ARL₀). Formulas are also provided for choosing k and h from prespecified values of the in-control and out-of-control average run lengths.     

Control Charts for the Mean and Variance based on Changepoint Methodology

This article develops a control chart for the mean and variance of a normal distribution based on changepoint methodology. A Bayesian approach is used to incorporate parameter uncertainty. The resulting control chart plots the probabilities of “no change” as samples become available at the monitoring stage. Average run length considerations are used to set the control limits. Simulations are used to compare the proposed chart with a more traditional Shewhart-type combined control chart for the mean and variance.     

空气质量指数监控与预测的控制图方法

世界上多数国家都采用空气质量指数这一指标衡量空气质量状况,对空气质量的有效监测和预警是解决空气污染的重要参考依据.本研究使用ARMA模型拟合空气污染指数(API)时序数据,通过模型残差建立控制图,根据控制图的变化监控并预警.研究采用2010年上海世博会API作为可控状态建立控制限,以2011年1～8月上海API数据建立ARMA(1,1)模型,通过2011年9月上海API模型预测与残差控制图证实模型和控制图的有效性.     

CUSUM和Cuscore控制图平均运行长度上界的估计

平均运行长度(ARL)是判断一类控制图监测变点效果好坏的重要工具.文章首先给出了特征指数取值(0,1)且均值不为常数时CUSUM控制图在Levy稳定过程中ARL上界的估计,改进了均值为常数时的结论;随后给出了特征指数取值(0,1)且均值不为常数时Cuscore控制图在Levy稳定过程中ARL上界的近似估计,完善了特征指数取值(0,2]时Cuscore控制图ARL的估计;最后通过数值模拟比较了两种控制图在监测Levy稳定过程均值变点中的效果和差异,结果表明Cuscore控制图比CUSUM控制图的监测效果好.