Authors: Philippe Castagliola; Fernanda Otilia Figueiredo
Addresses: LUNAM Université, Université de Nantes and IRCCyN UMR CNRS 6597, Nantes, France ' Faculdade de Economia da Universidade do Porto and CEAUL, Rua Dr. Roberto Frias 4200-464, Porto, Portugal
Abstract: A modified median chart with estimated control limits is proposed for monitoring the mean value of a normal process. The estimates for the nominal process parameters used to set up the control limits in Phase I are the average of the sample medians and the average of the sample ranges of m initial subgroups of size n. The run length properties of the chart are examined, and the obtained results lead us to conclude the proposed chart present an interesting RL performance (at least for an adequate choice of the chart parameter used to determine the control limits). Control chart parameters are provided for a specific in-control average run length of 370.4 for several combinations of n and m, which facilitates the use of the chart by practitioners, and an illustrative example of implementation of the chart is presented. Some recommendations are also given about the minimum number of initial subgroups m that must be considered to implement the chart with the constant parameter used in the case of known nominal values, and in order to obtain the expected performance. [Received 24 August 2011; Revised 28 October 2011; Accepted 13 February 2012]
Keywords: control charts; conditional run length; average run length; order statistics; median charts; estimated parameters; industrial engineering; statistical process control; SPC; estimated control limits.
European Journal of Industrial Engineering, 2013 Vol.7 No.5, pp.594 - 614
Received: 08 May 2021
Accepted: 12 May 2021
Published online: 28 Oct 2013 *