关键词: VSSI EWMA控制图, 平均产品长度, 经济统计设计, 预防维修, 比较分析

Abstract: With the rapid development of science and technology, the competition between enterprises is becoming fiercer. To gain competitive advantage, enterprises must produce high-quality products to meet the needs of customers. The control chart and maintenance management are two kinds of quality management tools commonly used in modern production and manufacturing process. The control chart mainly monitors the production process through the statistical principle to obtain the potential fault information in the production process, so as to guide the corresponding maintenance strategy. Meanwhile, preventive maintenance can prevent the further deterioration of the production system. The influence of the two on product quality and production cost is closely related. In view of the fact that the dynamic exponential weighted moving average (EWMA) control chart can quickly monitor the small and medium deviations occurring in the production system, in this context, the variable sampling size and sampling interval exponential weighted moving average (VSSI EWMA ) control chart is used to monitor the mean deviations occurring in the product quality characteristics of the production system, and the corresponding maintenance strategies are formulated according to the monitoring results of the control chart. The joint optimization design model of VSSI EWMA mean control chart and preventive maintenance is established from two aspects of economic performance and statistical performance, so as to effectively reduce the production cost and improve the product quality of enterprises.
In order to monitor the mean deviation of the quality characteristics of the product due to equipment abnormality in the production system, a joint optimization design of VSSI EWMA control chart and preventive maintenance is proposed. As an accurate assessment of monitoring efficiency, average product length (APL) is calculated by using the Markov chain method as the monitoring efficiency evaluation index of the statistical performance of the control chart. On the basis of analyzing three renewed scenarios determined by the joint design of preventive maintenance and control chart, average quality cost per product is calculated as a more precise indicator for economic evaluation. Taking average product length and average quality cost per product as objective functions simultaneously, a joint economic-statistical multi-objective optimization design model of VSSI EWMA control chart and preventive maintenance is constructed. Using non-dominated sorting genetic algorithm-III(NSGA-III), the calculation steps of the optimization design model are illustrated by a specific example, and the sensitivity of the main parameters of the model is analyzed. Finally, the model is compared with several existing joint design of EWMA control chart and planned maintenance. The results show that the optimization design method proposed in this paper has good performance in both statistical monitoring efficiency and economic quality cost.
The control chart used in this paper is a unitary control chart for monitoring individual quality characteristics of products. With the diversified trend of customer demand, enterprises need to produce products with multiple quality characteristics. Therefore, there is still room for further improvement in the monitoring performance of VSSI EWMA control charts. Subsequent studies will consider the use of multiple dynamic control charts to monitor the production process to achieve more comprehensive dynamic monitoring.

Key words: VSSI EWMA control chart, average product length, economic-statistical design, planned maintenance, comparative analysis