Estudo comparativo entre o gráfico de controle simultâneo (X-BARRA,S) e os gráficos de Shewhart para média e desvio-padrão

Abstract

Control charts are tools from Statistical Process Control widely used to monitor key quality characteristics of a product or service. For being extremely efficient in monitoring and improving quality, research is needed to investigate different approaches. However, the diversity of control charts and application methodologies makes the selection of the best combination to implement in a process harder. Furthermore, some works shows a few or no comparison between related subjects, making the selection even harder. The simultaneous (X-bar,S) control char is a case where the presented comparison raise doubts about is effectiveness even compared to Shewhart charts for mean (X-bar) and standard deviation (S). Therefore, this study aims to compare Shewhart control charts for mean (X-bar) and standard deviation (S) with the simultaneous (X-bar,S) chart in terms of ease of identifying the process state, performance with the average run length (ARL), and ability to determine when the deviation occurred in the sample series. To do so, the procedures for constructing control charts were presented, data were simulated to calculate the NMA, and a visual evaluation of the information presented in the charts was carried out. As a result, the innovations presented in the simultaneous (X-bar,S) chart shows inferior advantages compared to traditional Shewhart charts.