SPC Statistica Prcess Cntr文档.ppt

Selecting rational samples Chosen so that variation within the sample is considered to be from common causes Special causes should only occur between samples Special causes to avoid in sampling passage of time workers shifts machines Locations * Chart advice Larger samples are more accurate Sample costs money, but so does being out-of-control Don’t convert measurement data to “yes/no” binomial data (X’s to P’s) Not all out-of control points are bad Don’t combine data (or mix product) Have out-of-control procedures (what do I do now?) Actual production volume matters (Average Run Length) * Have you ever… Shot a rifle? Played darts? Played basketball? Shot a round of golf? What is the point of these sports? What makes them hard? * Have you ever… Shot a rifle? Played darts? Shot a round of golf? Played basketball? Emmett Jake Who is the better shot? * Discussion What do you measure in your process? Why do those measures matter? Are those measures consistently the same? Why not? * Variability Deviation = distance between observations and the mean (or average) Emmett Jake Observations 10 9 8 8 7 averages 8.4 Deviations 10 - 8.4 = 1.6 9 – 8.4 = 0.6 8 – 8.4 = -0.4 8 – 8.4 = -0.4 7 – 8.4 = -1.4 0.0 8 7 10 8 9 * Variability Deviation = distance between observations and the mean (or average) Emmett Jake Observations 7 7 7 6 6 averages 6.6 Deviations 7 – 6.6 = 0.4 7 – 6.6 = 0.4 7 – 6.6 = 0.4 6 – 6.6 = -0.6 6 – 6.6 = -0.6 0.0 7 6 7 7 6 * Variability Variance = average distance between observations and the mean squared Emmett Jake Observations 10 9 8 8 7 averages 8.4 Deviations 10 - 8.4 = 1.6 9 – 8.4 = 0.6 8 – 8.4 = -0.4 8 – 8.4 = -0.4 7 – 8.4 = -1.4 0.0 8 7 10 8 9 Squared Deviations 2.56 0.36 0.16 0.16 1.96 1.0 Variance * Variability Variance = average distance between observations and the mean squared Emmett Jake Observations 7 7 7 6 6 averages Deviations Squared Deviations 7 6 7 7 6 * Variability Variance = average distance between observations and the mean squar