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Nonparametric control chart for the range

  • US 6,718,221 B1
  • Filed: 05/21/2003
  • Issued: 04/06/2004
  • Est. Priority Date: 05/21/2002
  • Status: Expired due to Fees
First Claim
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1. A method for establishing a control limit for variability of a manufacturing process parameter, comprising:

  • measuring the parameter over a predetermined period of time;

    assembling a dataset having a plurality of datapoints, wherein each datapoint represents an individual measured value of the parameter;

    rank-ordering the datapoints within the dataset;

    selecting at least one subset of the dataset, wherein the subset is a predetermined number of datapoints including a high measured value and a low measured value defining a range of measured parameter values;

    calculating all possible numbers of a subsample of the dataset having the range defined by the subset;

    repeating the previous steps of selecting a subset and calculating all possible numbers of subsamples of the dataset having the range defined by the subset, until all possible numbers of ranges have been calculated for all possible subsets of the predetermined size within the dataset to define a set of ranges;

    rank-ordering the defined set of ranges; and

    establishing the control limit for the manufacturing process, defined by an upper limit and a lower limit wherein the upper and lower limits are a predetermined percentile of the rank-ordered set of ranges.

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