考虑延迟监测的预防维修和EWMA方差控制图联合决策模型

Joint decision-making model of preventive maintenance and EWMA chart for monitoring process variance based on delayed monitoring

针对设备异常将导致过程质量方差发生漂移的可修系统,提出了一种考虑延迟监测的预防维修和EWMA方差控制图联合决策模型。首先分析确定了预防维修和过程质量监控联合决策生产系统在延迟监测条件下形成的6种更新策略;然后基于每个抽样间隔期的分析思路,建立了每种更新策略的期望周期和成本,并根据更新过程理论构建了联合优化延迟监测期、预防维修规划周期及EWMA方差控制图参数(样本量、抽样间隔、控制线系数及平滑系数)以实现单位时间期望总成本最小的经济决策模型。实例分析表明,模型由于充分考虑了延迟监测问题,能够获得比不考虑延迟监测模型更优经济效益的决策结果。

A joint decision-making approach to preventive maintenance and Exponentially Weighted Moving Average ( EWMA) chart for monitoring process variance was developed. The proposal of delayed monitoring policy postponed the sampling process till a scheduled time and contributed to six renewal scenarios of the production process, where downtime was triggered by scheduled preventive maintenance period or the alert of EWMA chart proposed to monitoring the shift of process variance resulted by fault. The cycle cost and the cycle time of each scenario were obtained by integral calculation based on the analysis of each sampling interval. Therefore, a mathematical model was given to minimize the expected cost per unit time by optimizing values of six variables (scheduled duration without monitoring, scheduled preventive maintenance period, sample size, sampling interval, control limit and smoothing parameter). The results of a case indicate that the hourly cost of the proposed model is lower than that of the previous method used in the enterprise where delayed monitoring was not considered.