Artigo
Attribute charts for monitoring the mean vector of bivariate processes
Registration in:
Quality And Reliability Engineering International. Hoboken: Wiley-blackwell, v. 31, n. 4, p. 683-693, 2015.
0748-8017
10.1002/qre.1628
WOS:000354883900013
Author
Ho, Linda Lee
Costa, Antonio [UNESP]
Abstract
This article proposes two Shewhart charts, denoted np(xy) and np(w) charts, which use attribute inspection to control the mean vector ((x); (y)) of bivariate processes. The units of the sample are classified as first-class, second-class, or third-class units, according to discriminate limits and the values of their two quality characteristics, X and Y. When the np(xy) chart is in use, the monitoring statistic is M=N-1+N-2, where N-1 and N-2 are the number of sample units with a second-class and third-class classification, respectively. When the np(w) chart is in use, the monitoring statistic is W=N-1+2N(2). We assume that the quality characteristics X and Y follow a bivariate normal distribution and that the assignable cause shifts the mean vector without changing the covariance matrix. In general, the synthetic np(xy) and np(w) charts require twice larger samples to outperform the T-2 chart. Copyright (c) 2014 John Wiley &Sons, Ltd. Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Univ Sao Paulo, Dept Prod Engn, BR-05508900 Sao Paulo, Brazil Univ Estadual Paulista, Dept Prod Engn, Sao Paulo, Brazil Univ Estadual Paulista, Dept Prod Engn, Sao Paulo, Brazil
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