Solving Problems with Poka Yoke

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Many problems can be solved using mistake proofing approaches that are embodied in the five Poka Yoke principles that both detect and prevent errors from occurring.

Quick reference

Solving Problems with Poka Yoke

Many problems can be solved using mistake-proofing approaches that are embodied in the five Poka Yoke principles that both detect and prevent errors from occurring.

When to use

Poka Yoke principles can be applied at any time. They are often used during the Improve phase of a Lean Six Sigma project as part of the improvement actions. Different Poka Yoke principles are better suited to different types of improvement needs and constraints.

Instructions

Poka Yoke is the Japanese term for mistake proofing or error proofing. It is a set of design principles that is used to set a direction for product improvement or process design so that fewer errors are made. Essentially, the product or process “self-inspects” because the Poka Yoke feature either prevents the mistake or makes it so very obvious that it is immediately corrected before going on to the next step.

The Poka Yoke principles can be applied both at a full process or product level or at a more focused process step of feature level. They are used to start brainstorming discussions to develop solutions. In most situations, only two or three of the principles lead to solutions. The Poka Yoke principles are:

Physical Characteristics

This principle relies on using some physical aspect of the product or item that is to be created to guide the product correctly through the process or ensure correct operation of the product. This includes characteristics such as size (too big or too small to fit), shape (round peg will not go in the square hole), color (red to red, blue to blue), weight (too heavy or too light), or any other physical characteristic. This technique is often used in product design prior to design freeze.

Error Detection Sensors

Some aspect of the process or product has an embedded sensor that is able to detect when an error has occurred. Often, this will stop the process and create an error message that must be addressed by the operator before they can continue with the process. This approach is commonly used with online forms and applications, although it can be used with physical systems that have embedded sensors. This technique is normally applied at process steps to improve the First Pass Yield at that step.

Equipment and Tooling Positioning

This is the favorite approach of manufacturing and process engineers. In this approach, the product does not change and even the process step activities do not change. Rather there is some type of operator aid, tool, or piece of equipment that either guides the process step activity, or provides an immediate indication of the quality status of the process step results. An example of this is the use of Go/No Go gauges. While not necessarily 100% effective, it is a very fast and easy approach and can normally create significant improvement.

Counters

This is the easiest of the principles to apply. Find something in the process that is countable and related to the correct operation of a process step and count it. You could be counting time units, # of items, weight, or any other countable parameter. Again, this may not provide a 100% improvement, but it often leads to an 80% to 90% improvement which is still quite good. It can be applied in both the product and the process improvement approaches.

Checklists of Templates

This approach uses checklists or templates to guide the operator or user to take the correct actions. It can be very helpful, provided it is available at the point of use and the individual actually follows it. This technique works best with processes that are only occasionally used. Most people will start to ignore these for routine operations that they do frequently.

Hints & tips

  • When using Poka Yoke principles, I clarify the problem, then ask the brainstorming team to try to think of at least one idea for improvement using each of the five principles. Our final solution will often be a combination of several ideas.
  • This is not a statistical or mathematical technique. It relies on the judgment and experience of those using it to apply these principles wisely and well to the problem. They work best with subject matter experts participating in the implementation.
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  • 00:05 Hi I'm Ray Sheen, and now I'd like to discuss the use of Poka Yoke principles
  • 00:09 when designing the solution of your problem.
  • 00:13 You may be saying to yourself, Poka what?
  • 00:16 Well, Poka Yoke is the Japanese term for mistake proofing or error proofing.
  • 00:19 It was made popular in Japanese auto manufacturers in the 1990s.
  • 00:25 A Poka Yoke feature can be either in the design of the product or the process.
  • 00:29 It is anything that either prevents a mistake from occurring or
  • 00:32 detects it immediately and prevents the product from being used or
  • 00:35 the process continuing until the mistake is corrected.
  • 00:38 It essentially lets the product or process self-inspect.
  • 00:42 What is great is that you get 100% inspection without adding any inspectors.
  • 00:47 Poka Yoke is not a mathematical analysis or matrix manipulation,
  • 00:51 it is a set of five principles.
  • 00:54 Once you have identified the problem, you then brainstorm using the five principles
  • 00:58 to determine what type of Poka Yoke features could be used to reduce or
  • 01:02 prevent the problem.
  • 01:04 I'll go through each of these five principles in the next few slides.
  • 01:08 First is the principle of physical characteristics.
  • 01:10 This is normally used with products and
  • 01:12 it's best used during the design of the product or system.
  • 01:15 It is often very difficult to apply this after the design is complete.
  • 01:19 With this principle, there's some physical characteristic that will indicate
  • 01:23 an error status or ensure the product or system is used correctly.
  • 01:28 This characteristic could be size, shape, color, weight, or
  • 01:31 any other physical characteristic, or even a combination of these.
  • 01:35 Let's look at a few examples.
  • 01:36 The pin on the right is symmetrical, so you can't possibly put it in upside down.
  • 01:41 This plate needs to have an asymmetrical bolt hole pattern.
  • 01:44 The plate on the left is symmetrical, so it could be put in backwards and
  • 01:48 the holes would not line up.
  • 01:50 The plate on the right has exaggerated asymmetry.
  • 01:53 The interfacing parts can accommodate that asymmetry and
  • 01:56 the plate cannot be put in backwards.
  • 01:59 The washer on the right drops into a slot so that the holes will be aligned.
  • 02:04 The slot holds it in its place.
  • 02:07 The second principle is error detection sensors.
  • 02:10 This approach uses some type of sensor technology to determine if the product or
  • 02:14 process is proceeding as it should.
  • 02:16 The sensor can detect if something is wrong and
  • 02:19 often is now used to highlight what should be done next?
  • 02:22 This has become the preferred method for
  • 02:24 applying Poka Yoke in any type of computer interface.
  • 02:27 Let's use the Uber webpage as an example.
  • 02:31 If I go to this page and try to sign up by providing just my name, but
  • 02:35 not my email or phone number,
  • 02:36 while i get an error message telling me to complete the blank field.
  • 02:41 The web page has used the error detection sensor to determine that the application
  • 02:46 is not complete and it will not let me proceed until I get it right.
  • 02:50 The next principle is tooling and equipment positioning.
  • 02:53 Just like physical characteristics is popular with product designers,
  • 02:57 this principle is popular with process designers.
  • 03:00 In fact, this is the most common principle I have used with Lean Six Sigma projects
  • 03:04 in the manufacturing environment.
  • 03:07 With this principle, there is some aspect of the tooling or
  • 03:10 equipment design that either guides the work item correctly through the process or
  • 03:15 is used to check to be certain that the item is correct.
  • 03:18 This is the principle behind go-no-go gauging in manufacturing.
  • 03:22 The great thing about this principle is that does not require that you change
  • 03:26 the design of the product.
  • 03:28 Instead, it creates a tool or
  • 03:29 shop aid that will help work with the processing of the product.
  • 03:34 In my example here, I have two gears that must be precisely positioned on a shaft.
  • 03:39 I can put them on the shaft and measure the position, reposition, and remeasure,
  • 03:43 repeating this until I finally get it correct.
  • 03:46 Or I just put the shaft into this fixture, use this locating block to make sure
  • 03:50 that the shaft is at the correct location and then just slide the gears on and
  • 03:55 tighten them down, they will be positioned correctly.
  • 03:59 The next principle is to count something in the product or process.
  • 04:02 In this case, you might count the number of work pieces before maintenance is
  • 04:06 required, the amount of time for a chemical process to occur,
  • 04:09 the weight of a package to be sure that the correct quantity is in the box or
  • 04:13 anything else that is countable.
  • 04:16 A high count or low count says that something is wrong and
  • 04:19 it needs to be investigated.
  • 04:21 This principle is often the easiest one to use.
  • 04:24 It seldom will give 100% accuracy, but can often provide significant improvement.
  • 04:30 So in my example, the organization kitted the assembly of the item and
  • 04:33 provided just the right number of bolts.
  • 04:36 If I have any left over, I forgot to install something.
  • 04:39 The bolt count is the Poka Yoke.
  • 04:42 The final principle is checklists and templates.
  • 04:46 This principle is easy to understand.
  • 04:48 A checklist or template is created that provides direction to the operator on what
  • 04:52 to do next and how things should look when that step is done.
  • 04:56 That checklist could be a manual one or an automated checklist, much like personal
  • 05:00 tax software takes you through all the steps to create your income tax submittal.
  • 05:05 In my experience, this technique works best for
  • 05:08 processes that are followed infrequently, then they provide excellent guidance.
  • 05:13 But when it is a routine process that's being done dozens of times a day,
  • 05:17 the individual becomes numb to the checklist and they don't really follow it.
  • 05:22 Anybody can make a mistake, well, the Poka Yoke principles
  • 05:27 are great ways to get that 100% inspection of the product or
  • 05:32 process without adding 100% inspectors.

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