Polyhedrika

  Value streams require real time data collection in order to control them. This is often done automatically by the equipment itself but in some occasions it must be done manually.  In spite of the high-tech of our shop floors you can still see pencil and paper data collection being used. https://youtu.be/C7chwW_cXbc Unfortunately, detecting aspect defects is often difficult to automate even with AOI (Automatic Optical Inspection). When an operator is required to inspect we need a method to enter the results into the system. Line incidents, change of critical process parameters, etc. also need to be reported the moment they take place. Pencil & Paper Reporting The method still widely used in this 21st century is: The operator hand writes the defect data on a form Forms are collected at the end of the shift A clerk types the forms contents into the system at a later stage The engineer analyses the results and takes corrective actions well after the data was entered. Thi...

  Statistical Process Control (SPC) is used to control a critical process output acting on the factors affecting it only when required. The purpose is to differentiate  between a statistically significant change in the process and common cause variation because the actions required will be different. Real Time Statistical Process Control enables the operators running the process to know when action is required, as described in    Real Time SPC There are two extremes to avoid:            Over-reaction (adjusting after every output) makes the process worse: dispersion is increased. Under-reaction is just as bad: a slow process degradation passes undetected until it is too late. SPC Charts for Variables and Attributes We will now analyse some of the charts used for variables and attributes. SPC Chart Interpretation SPC uses some rules, developed by the Western Electric company, to detect symptoms of  statistically significant ...

     Statistical Process Control is used to detect when a significant change has taken place in a process.  We want to detect this change as soon as possible. What is real-time will depend on the process.  All processes have variation as observed in any of their metrics but not all variation is significant from the statistical point of view.  Random Variation Vs Trends: Statistical Process Control When we want to control a process by adjusting some process parameter we can make two mistakes: Over-react by adjusting when we shouldn't Under-react by failing to adjust when we should Control over-reaction A case of over-reaction is illustrated by the following example: Someone is shooting at a target and, based on the deviation of the impacts, he adjusts the gun site after each shot. The end result will be an increase of the dispersion of the impacts, therefore the adjustments will make the process worse. The correct way is, of course, to fire 5 or 6 shots with...