中文摘要：

针对过程数据存在异常值的问题，采用中位数统计量（X）代替传统均值（X）统计量，提出一种变采样间隔X（Variable Sampling Interval X，VSIX）控制图来监控过程均值偏移。首先推导出VSIX控制图的平均报警时间和报警时间标准差等性能指标；保证过程处于受控状态的统计性能指标，得到VSIX控制图的最优决策变量，进一步获得其失控状态下的最优性能指标。仿真结果表明，VSIX控制图的性能明显优于传统X控制图，当过程均值偏移较小时，其优势更加明显。

英文摘要：

Considering the outliers in the process samples, the median（X-）is used instead of the mean（X）and a variable sampling interval X （VSI X ）chart is proposed to monitor the process mean. First, we drive the expressions of the average time to signal （ATS）and the standard deviation of the time to signal（SDTS）of the VSI X chart. The optimal parameters of the VSI X chart are obtained through the constraints on the in-control properties of the chart. The out-of-control properties（ATS,SDTS）of the VSI X chart are calculated with these optimal parameters.The simulation results showed that the VSI X chart always performs better than the X chart, especially for smaller mean shifts.