Evaluation of the stability of paper basis-weight profiles using multivariate time series

In the papermaking process, a major concern is maintaining uniform basis weight in the paper sheet. Basis weight, the weight per unit area of the paper, can vary as a function of both time and position across the width of the paper machine. In this short paper, a quantitative index for evaluating the stability, i.e., the similarity of consecutive basis-weight profiles taken across the width of a paper machine, is presented and used to analyze the stability of two production paper machines. The index is determined from autoregressive moving average multivariate time-series models developed for the profile data. With this approach, a more consistent estimate of basis-weight stability can be obtained with fewer profiles by removing the correlation imparted by the papermaking process. Moreover, the parameters of the model can be used to analyze possible sources of basis-weight instability.