【正文】 causal variables. The specific tool used is called the MultiVari chart. Measurement Time or Condition Change Overtime or Condition Within Piece Schematic of a Multivari Chart Between Pieces 9 Why Is It Useful? When Is it used ?Multivari analysis can help you narrow a list of potential causes to a much smaller list suitable for detailed investigation, through designed experiments, for example. It helps you focus your attention as you funnel down to find potential variables that you may need to study. ?In the Analyze step to plement process analysis and stratification. It usually follows stratification analysis. 10 When Should It Be Used? ?In the Analyze step to plement process analysis and stratification. It usually follows stratification analysis. 11 Planning a Multivari Study: Overview A. Preliminary work B. Main work Choose product characteristics relevant to the problem (from Define or Measure steps) Develop list of potential factors (causes) of variation in the characteristic of interest 7. Analyze the results 1. Define scope or domain of the study 2. Define time profile of the sample selection 3. Make a detailed plan for collection of the product samples 4. Collect the samples 5. Measure the samples 6. Plot the sample data 12 Families (Components) of Variation Typical families of variation in a manufacturing environment can be clustered together: Unit families: ?Within Unit variation: different measurements or results at different points within the unit or product ?UnittoUnit: one unit to the next (within subgroup variation) ?Subgroup to subgroup ?Streamtostream: suppliertosupplier, linetoline, machinetomachine, tooltotool, operatortooperator, etc. 13 Families (Components) of Variation, cont. Time families ?Shortterm to Longterm Measurement family ? Gage Ramp。 F a ct o r 4 : L I n eL i n e Sa m p l eChart Appearance Minitab plots the three samples in sequence left to right for line 1, 4/18/99 AM. The square shows the average of these three reading. The diamond is the average of all the readings within one day and line. 30 CrtlE or Stat Quality Tools MultiVari Charts… In the options window, connect the means for factors 13. Some people find it easier to see the relative contribution of the different families when the means are connected. Showing Changes in Average on the MultiVari Chart 31 4 / 1 8 / 9 9 4 / 1 9 / 9 9AMPMAMPM0 . 0 20 . 0 30 . 0 40 . 0 50 . 0 20 . 0 30 . 0 40 . 0 521D a t e1 2 3 F a ct o r 1 : Sa m p l e 。 two levels, AM and PM. ? Family 4: Longterm variation (day to day)。s) as well as output measures (Y39。s. 52 Illustration (1) Suppose the team in the paint thickness example had been able to record a pair of continuous X39。s output. 2. The team should record the time of day and information about press conditions (including shift and operators) that might provide additional clues. 3. When the team grabs samples at the low or high temperatures, it should also record the pressure at the same time. Similarly, when they grab samples at the low or high pressures, they should record the temperature. 4. Jumping right to observations on temperature and pressure may miss other signals that might be revealed by a more plete multivari analysis that considered within unit variation, unit to unit variation, subgroup to subgroup variation and longterm variation. Also, there may be other families of variation (related to geometry of units within the press, for example) relevant to the study. 5. Has the team verified the performance of the temperature and pressure gauges? 59 Summary Multivari analysis is a method that helps you depose total variation into ponent families. By means of a multivari graph, you seek to match patterns in the variation with potential causes. You use the method to narrow down potential causes and find clues as you build a useful causal theory. 60 Reflection Consider how you might apply Multivari analysis to your project. What questions do you have now about this method? 。s to guide your sampling approach ?Seek to observe the process when the X39。s at the same time you gather product samples and measure output characteristics ?Associate changes in X39。 here we select the two time families as factors 2 and 3 38 Minitab FollowAlong, Part 2, cont. Unless you check the first box, Minitab will only display the means of the first three factors. 39 Minitab FollowAlong, Part 2, cont. 4 / 1 9 / 9 94 / 1 8 / 9 9PMAMPMAM0 . 0 80 . 0 70 . 0 60 . 0 50 . 0 4D a t eFilmThicknesB a c k F r o n tM u l t i V a ri C h a rt f o r F i l mT h i ckn e s By Po si t i o n D a t eA M / P MP o si t i o n40 Minitab FollowAlong, Part 2, cont. 4 / 1 9 / 9 94 / 1 8 / 9 9PMAMPMAM0 . 0 80 . 0 70 . 0 60 . 0 50 . 0 4D a t eFilmThicknes123M u l t i V a ri C h a rt f o r F i l mT h i ckn e s By U n i t N a me D a t eA M / P MU n i t N a m e41 Alt