Using an MQE chart based on a self-organizing map NN to monitor out-of-control signals in manufacturing processes

Abstract

Control charts are recognized as one of the most important tools for statistical process control (SPC), used for monitoring any abnormal deviations in the state of manufacturing processes. However, the effectiveness of control charts is strictly dependent on statistical assumptions that in real applications are frequently violated. In contrast, neural networks (NNs) have excellent noise tolerance in real time, requiring no hypothesis on the statistical distribution of monitored processes. This feature makes NNs promising tools for quality control. In this paper, a self-organizing map (SOM)-based monitoring approach is proposed for enhancing the monitoring of processes. It is capable of providing a comprehensive and quantitative assessment value for the current process state, achieved by minimum quantization error (MQE) calculation. Based on MQE values over time series, a novel MQE chart is developed for monitoring process changes. The aim of this research is to analyse the performance of the MQE chart under the assumption that predictable abnormal patterns are not available. To this aim, the performance of the MQE chart in manufacturing processes (including non-correlated, auto-correlated and multivariate processes) is evaluated. The results indicate that the MQE chart may be a promising tool for quality control.

Keywords:

• Statistical process control
• Neural network
• Self-organizing map
• Manufacturing process

Acknowledgements

This work was supported by the National Science Foundation of China under Grant 50675137 and the Program for New Century Excellent Talents in University of China (NCET 2006). The authors express sincere appreciation to the anonymous referees for their detailed and helpful comments to improve the quality of the paper. Thanks also go to Dr Wang Shijin for invaluable advice and encouragement.