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Prevention as Control
One of the best techniques for controlling a process to perform in a particular manner is to prevent it from performing in any other manner. There are methodologies that can be used to create prevention of process problems, Poky Yoke and Five S Disciplines.
When to use
When designing a solution in the Improve phase, Poka Yoke and Five S Disciplines should be considered. However, both are as much about a mindset change as a product or process design change; so they need to be trained and reinforced in the Control phase until they become part of the culture.
Lean Six Sigma is inherently a corrective action methodology because it seeks to solve an existing problem. However, the solution can and should include elements of preventive action which would act as a barrier against future problems. There are two methodologies that are preventive action enablers and both can be used in the design and implementation of the Lean Six Sigma solution.
Poka Yoke means mistake proofing or error proofing. It consists of elements of a product or process design that either prevent a mistake from occurring or make the mistake immediately obvious to the operator or user, so that they fix it before they continue with the process or use the product. Poka Yoke is a principle-based methodology, so there are no formulas or statistics. The five Poka Yoke principles are:
- Part Characteristics – An attribute of the part, such as size, shape, or color, are used to direct the operator or user. Example: Square peg cannot go in a round hole.
- Error Detection Sensors – Added detection sensor or inspection step that warns the operator or user that an error has just occurred. Example: A continuity check for a wiring step to make sure all the wires are connected.
- Equipment and Tooling Positioning – The design of tooling, equipment or fixtures so that it assembles correctly and guides the work piece to the proper location. Whereas the part characteristic principle involved part redesign, this principle does not redesign the part but rather redesigns what handles the part. Example: Equipment for fabricating items will not start if there is no raw material on the work surface.
- Counters – An attribute of the process or product is counted to ensure that it is operating correctly. Example: A timer counts the minutes for a drying operation before the work piece can move to the next step.
- Template and Checklists – A template or checklist is used to guide the operator or user on what to do next. Example: A setup and installation guide accompanying a new computer.
Five “S” Disciplines
The Five “S” Disciplines are a workplace organization methodology. By cleaning and organizing the workplace, the chance to introduce special cause errors into the process is reduced and it is easier to see when a process problem is occurring. When the disciplines have been fully implemented, they become a mindset and culture for the organization. These Five "S" disciplines should be followed in the order shown.
- Sort (Seiri) – Sort all the items found in the work place and group them by use. If not required in the workplace, return them to the appropriate location.
- Set in Order (Seitton) – Organize the remaining items to put them in logical order as they are used. Design the work station for efficiency. This is sometimes called Straighten.
- Shine (Seiso) – Clean and maintain the workplace and all equipment. This minimizes breakdowns and contamination of work items.
- Standardize (Seiketsu) – Create standard procedures and standard operations where appropriate. Standardize the workstation for tools, parts and equipment storage so that the operator always knows where to find and store everything.
- Sustain (Shitsuke) – Once the first four disciplines are in place, perform periodic audits and training to maintain the disciplines.
Hints & tips
- Work with the process operators to get their insight on the most difficult steps. These should be the first candidates for Poka Yoke.
- The Templates and Checklists principle works best for occasional processes. Operators have a tendency to get “numb” to checklists on routine items, so avoid this approach for frequent routine processes.
- When implementing Five S, ensure that you include the operators in the discussion and the activity, so that it does not appear to be used as disciplinary process against them.
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