A new statistical high-quality process monitoring method: The counted number between omega-event control charts

Control chart techniques for high-quality process have attracted great attention in modern precision manufacturing. Traditional control charts are no longer applicable because of high false alarm rate. To solve this problem, in this article a new statistical process monitoring method, the counted number between omega-event statistical process control charts, abbreviated as CBω charts, is proposed. The phrase omega event denotes that one observation falls into some certain interval and the CBω chart is to monitor the number of consecutive parts between successive r omega events. On the basis of CBω charts, a dual-CBω monitoring scheme is developed. This scheme sets up two CBω charts with symmetrical omega events, (μ+δ,+∞) and (-∞,μ-δ), respectively. The performance of CBω charts and dual-CBω monitoring is investigated. Dual-CBω monitoring has shown its capability in detecting both mean and variance shift and convenience in implementation compared with other traditional charts. Dual-CBω monitoring can reduce false alarm rate greatly without introducing an unacceptable loss of sensitivity in detecting out-of-control signals in high-quality process control.