Process shift modes

The mean shifts (or range shifts, standard deviation shifts) of a process may be classified into a set of modes (or classifications), each of which is characterized by the shift magnitude (δ) and the occurrence probability, f. The knowledge relating to the shift modes is useful to the improvement of the effectiveness of the control charts and to the reduction of the cost of SPC (statistical process control). Presents an approach to estimate δ and f of the shift modes, using the sample data from the SPC and adopts a clustering method to classify different shift modes. Finally, describes an example of the application of the estimated shift modes.